Applications of light-emitting nanoparticles

ABSTRACT

A method for the production of a robust, chemically stable, crystalline, passivated nanoparticle and composition containing the same, that emit light with high efficiencies and size-tunable and excitation energy tunable color. The methods include the thermal degradation of a precursor molecule in the presence of a capping agent at high temperature and elevated pressure. A particular composition prepared by the methods is a passivated silicon nanoparticle composition displaying discrete optical transitions.

This application claims priority to Provisional Patent Application No.60/302,594 entitled “Light-Emitting Nanocrystals” filed on Jul. 2, 2001.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The United States Government has rights in this invention pursuant toNational Science Foundation Contract No. 26-1122-20XX.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of nanotechnology. Inparticular, to compositions and methods of making Group IV metalnanoparticles and their applications.

2. Description of the Relevant Art The term “nanoparticle” generallyrefers to particles that have an average diameter between about 1 nm to100 nm. Nanoparticles have an intermediate size between individual atomsand macroscopic bulk solids. Nanoparticles typically have a size on theorder of the Bohr exciton radius, or the de Broglie wavelength, of thematerial, which allows individual nanoparticles to trap individual ordiscrete numbers of charge carriers, either electrons or holes, orexcitons, within the particle. The spatial confinement of electrons (orholes) by nanoparticles is believed to alter the physical, optical,electronic, catalytic, optoelectronic and magnetic properties of thematerial. The alteration of the physical properties of a nanoparticledue to confinement of electrons is generally referred to as quantumconfinement effects.

Nanoparticles may exhibit a number of unique electronic, magnetic,catalytic, physical, optoelectronic and optical properties due toquantum confinement effects. For example, many nanoparticles exhibitphotoluminescence effects that are significantly greater than thephotoluminescence effects of macroscopic molecules having the samecomposition. Additionally, these quantum confinement effects may vary asthe size of the nanoparticle is varied. For example, size-dependentdiscrete optical and electronic transitions exist for clusters of GroupII-VI semiconductors (e.g., CdSe) or Group III-V semiconductors (e.g.,InAs). This loss of energy level degeneracy, however, has not previouslybeen observed in the optical properties of Group IV nanoparticles (e.g.,silicon (Si) nanocrystals). In Si, for example, the lowest lyingenergetic transition violates conservation of momentum; therefore, lightabsorption requires phonon assistance (a phonon is a quanta ofvibrational energy), resulting in a very low transition probability.Consequently, bulk Si photoluminescence is very weak. Quantumconfinement in Si nanocrystals and porous Si, however, leads to enhancedluminescence efficiencies with quantum yields that have reached as highas 5% at room temperature and blue-shifted “band gap” energies. However,in sharp contrast to their direct band gap semiconductor counterparts,Si nanocrystals have not displayed discrete electronic transitions inthe absorbance and photoluminescence excitation (PLE) spectra.

The wet chemical techniques used to synthesize Group II-VI and III-Vsemiconductors have not been readily applied to Group IV materials,largely due to the high temperatures required to degrade the necessaryprecursors. Typically the temperature required to degrade the necessaryGroup IV precursors exceeds the boiling points of typical solvents.Furthermore, the strong covalent bonding of Si requires temperatureshigher than the Group II-VI materials to achieve highly crystallinecores. Moderate progress has been made with alternative solution-phasereduction of Si salts and aerosol methods. These methods, however, haveproduced nanocrystals with extremely broad size distributions. Aerosolmethods have required a thick oxide coating to stabilize theirstructure, which has been shown recently to significantly affect thephotoluminescence (PL) energies of porous Si.

SUMMARY OF THE INVENTION

In an embodiment Group IV metals form nanocrystalline or amorphousparticles by the thermal degradation of a precursor molecule in thepresence of molecules that bind to the particle surface, referred to asa capping agent at high temperature and elevated pressure. In certainembodiments, the reaction may run under an inert atmosphere. In certainembodiments the reaction may be run at ambient pressures. The particlesmay be robust, chemically stable, crystalline, or amorphous andorganic-monolayer passivated, or chemically coated by a mixture oforganic molecules. In one embodiment, the particles emit light in theultraviolet wavelengths. In another embodiment, the particles emit lightin the visible wavelengths. In other emobodiments, the particles emitlight in the near-infrared and the infrared wavelengths. The particlesmay emit light with high efficiencies. Color of the light emitted by theparticles may be size-tunable and excitation energy tunable. The lightemission may be tuned by particle size, with smaller particles emittinghigher energy than larger particles. The surface chemistry may also bemodified to tune the optical properties of the particles. In oneembodiment, the surfaces may be well-passivated for light emission athigher energies than particles with surfaces that are notwell-passivated. The average diameter of the particles may be between 1and 10 nm. A particular composition prepared by the methods is apassivated silicon nanoparticle composition displaying discrete opticaltransitions and photoluminescence.

In an embodiment, a solvent may be used to assist in solvating theprecursors and capping agents. The solvent may be substance capable ofdissolving the precursor and capping agents. The capping agent may actas the solvent.

In certain embodiments, the nanoparticles may include capping agents.The capping agents may include an end bound to the surface of theparticle. Capping agents may assist in protecting the particle fromoxidation and/or water. Capping agents may assist in solubilizing, ordispersing, the particles. In one embodiment, polar capping agents mightbe used to disperse particles in aqueous media. In another embodiment,organic, largely hydrocarbon, capping agents might be used to disperseparticles in organic solvents. In another embodiment, a mixture of polarand organic capping agents may be used to disperse the particles in apolar organic solvent. In another embodiment, fluorinated capping agentsmay be used to disperse the particles in carbon dioxide, or otherfluorocarbon solvents. Capping agents may assist in controlling theformation of the particles during the reaction, by decreasingaggregation of the particles as the particles form.

In some embodiments, a flow through processor may be used to form thenanoparticles. The processor may allow for the continuous production ofparticles on a large scale.

In certain embodiments, the nanoparticles formed by the method describedherein may be used in a variety of applications. Several examples ofpossible applications are described herein and include: lights; lightemitting diodes; flat panel displays; biological assays; biologicalsensors; memory devices; and transistors. The methods described hereinmay create Group IV particles with novel properties.

In an embodiment, a method of forming nanoparticles may include heatinga mixture of a Group IV metal organometallic precursor and a cappingagent at a temperature where the precursor decomposes forming thenanoparticles.

In some embodiments, it should be understood that heating the mixture inorder to decompose the precursors to form nanoparticles may includeheating at a temperature at or below the supercritical temperature ofthe capping agent or a solvent (in embodiments where the capping agentdoes not act as the solvent).

In certain embodiments, it should be understood that heating the mixturein order decompose the precursors to form nanoparticles may includeheating at a temperature above about 300° C. and below the supercriticaltemperature of the capping agent or a solvent (in embodiments where thecapping agent does not act as the solvent).

In other embodiments, it should be understood that heating the mixturein order to decompose the precursors to form nanoparticles may includeheating at a temperature below the supercritical temperature of thecapping agent or a solvent (in embodiments where the capping agent doesnot act as the solvent). The temperature may be not less than about 100°C. below the supercritical temperature of the fluid capping agent or asolvent (in embodiments where the capping agent does not act as thesolvent).

In an embodiment, a nanoparticle may be formed by a method includingheating a mixture of a Group IV organometallic precursor and a cappingagent. Heating the mixture may include heating the mixture at atemperature where the precursor decomposes forming the nanoparticle.

Certain embodiments may include a nanoparticle including a Group IVmetal and a capping agent coupled to the Group IV metal. Thenanoparticle may have an average particle diameter of between about 1 toabout 100 angstroms. The capping agent may inhibit oxidation of thenanoparticle.

An embodiment may include a method of forming nanoparticles includingheating a mixture of one or more organometallic precursors and a cappingagent in a supercritical fluid. The method may include decomposing theorganometallic precursors, forming the nanoparticles.

In some embodiments, a nanoparticle may be formed by a method comprisingheating a mixture of one or more organometallic precursors and a cappingagent in a supercritical fluid. The method may include decomposing theorganometallic precursors, forming the nanoparticles.

In an embodiment, a nanoparticle may include a metal and a capping agentcoupled to the metal. The nanoparticle may have an average particlediameter of between about 1 to about 100 angstroms. The capping agentmay inhibit oxidation of the nanoparticle.

Certain embodiments may include a method of forming nanoparticlesincluding heating a mixture of one or more metal salts and a cappingagent in supercritical water. The metal salts may decompose, forming thenanoparticles.

In other embodiments, a nanoparticle may be formed by the methodcomprising heating a mixture of one or more metal salts and a cappingagent in supercritical water. The metal salts may decompose, forming thenanoparticles.

In an embodiment, a nanoparticle may include a metal oxide and a cappingagent coupled to the metal oxide. The nanoparticle may have an averageparticle diameter of between about 1 to about 100 angstroms. The cappingagent may inhibit oxidation of the nanoparticle.

An embodiment of a method of forming nanoparticles in a continuousmanner may include injecting a mixture of an organometallic precursorand a capping agent into a reactor. The method may include heating themixture within the reactor to a temperature wherein the precursordecomposes forming the nanoparticles. In addition the method may includeremoving the formed nanoparticles from the reactor while substantiallysimultaneously injecting additional organometallic precursors andcapping agents into the reactor.

In certain embodiments, a nanoparticle may be formed by a methodincluding heating a mixture of one or more organometallic precursors anda capping agent in a fluid at a temperature above about 300° C. andbelow the supercritical temperature of the fluid.

In other embodiements, a nanoparticle may be formed by a methodcomprising heating a mixture of one or more organometallic precursorsand a capping agent in a fluid at a temperature below the supercriticaltemperature of the fluid. The temperature of the fluid may be not lessthan about 100° C. below the supercritical temperature of the fluid.

An embodiment of a light emitting device may include a plurality ofnanoparticles. The nanoparticles may include a Group IV metal and acapping agent coupled to the Group IV metal. The nanoparticles may havean average particle diameter of between about 1 to about 100 angstroms.The light emitting device may include an anode electrically coupled tothe plurality of nanoparticles. The light emitting device may include acathode electrically coupled to the plurality of nanoparticles. Theanode and the cathode together may be configured to conduct an appliedcurrent to the nanoparticles. The nanoparticles may produce light inresponse to the applied current.

An embodiment of a light emitting device may include a plurality ofnanoparticles. The nanoparticles may be formed by a method includingheating a mixture of a Group IV organometallic precursor and a cappingagent at a temperature. Heating the mixture may decompose the precursorforming the nanoparticles. The light emitting device may include ananode electrically coupled to the plurality of nanoparticles. The lightemitting device may include a cathode electrically coupled to theplurality of nanoparticles. The anode and the cathode together may beconfigured to conduct an applied current to the nanoparticles. Thenanoparticles may produce light in response to the applied current.

Certain embodiments of a display apparatus may include a support and aplurality of light emitting devices positioned on the support. The lightemitting devices may include a plurality of nanoparticles. Thenanoparticles may include a Group IV metal and a capping agent coupledto the Group IV metal. The nanoparticle may have an average particlediameter of between about 1 to about 100 angstroms. The light emittingdevices may include a conductive material electrically coupled to theplurality of nanoparticles. The conductive material may function toconduct an applied current to the particles. The display apparatus mayinclude a controller functioning to control the application of currentto each of the lights.

An embodiment of a system for detecting an analyte in a fluid mayinclude a nanoparticle. The nanoparticle may include a Group IV metaland a capping agent coupled to the Group IV metal. The metalnanoparticle may have an average particle diameter of between about 1 toabout 100 angstroms. The system may include a receptor which functionsto interact with the analyte. The receptor may be coupled to thenanoparticle.

An embodiment of a system for detecting an analyte in a fluid mayinclude a nanoparticle. The nanoparticle may be formed by a methodcomprising heating a mixture of a Group IV organometallic precursor anda capping agent. Heating the mixture may include heating the mixture ata temperature where the precursor decomposes forming the nanoparticle.The system may include a receptor which functions to interact with theanalyte. The receptor may be coupled to the nanoparticle.

An embodiment of a memory device which may include a source functioningto apply an electrical charge. The memory device may include a drainfunctioning to hold an electric charge. The memory device may include achannel functioning to separate the source and the drain. The memorydevice may include a floating gate positioned above the channel. Thefloating gate may include a plurality of nanoparticles. Where at least aplurality of the nanoparticles may include a Group IV metal and acapping agent coupled to the Group IV metal. At least one of thenanoparticles may have an average particle diameter of between about 1to about 100 angstroms. The memory device may include a control gatepositioned substantially adjacent the floating gate. The memory devicemay include and a conductor comprising an oxide positioned between thecontrol gate and the floating gate. The floating gate may be positionedbetween the channel and the control gate.

In an embodiment, a coherent light emitting device may include aplurality of nanoparticles. The nanoparticle may be formed by a methodincluding heating a mixture of a Group IV organometallic precursor and acapping agent at a temperature wherein the precursor decomposes, and thenanoparticle is formed. The nanoparticles may include a metal and acapping agent coupled to the metal. At least one of the nanoparticlesmay have an average particle diameter of between about 1 to about 100angstroms. The coherent light emitting device may include an excitationsource functioning to apply energy to the nanoparticles in an absorbableform. The coherent light emitting device may include an optical cavityfunctioning to direct light. When the excitation source applies energyto nanoparticles the nanoparticles may produce light. Light produced bythe nanoparticles may be directed by the optical cavity.

In an embodiment, a system for at least partially containing anelectrical charge temporarily may include a cathode comprising aplurality of nanoparticles. The nanoparticle may be formed by a methodincluding heating a mixture of a Group IV organometallic precursor and acapping agent at a temperature wherein the precursor decomposes, and thenanoparticle is formed. The nanoparticles may include a metal and acapping agent coupled to the metal. The metal may be a Group IV metal.At least one of the nanoparticles may have an average particle diameterof between about 1 to about 100 angstroms. The nanoparticles may beelectroactive. The system may include an anode. The anode may include anelectroactive material. The system may include a separator positionedbetween the cathode and the anode functioning to inhibit contact betweena portion of the cathode and a portion of the anode.

In an embodiment, a system for electrically communicating with abiological entity may include a nanoparticle. The nanoparticle may beformed by a method including heating a mixture of a Group IVorganometallic precursor and a capping agent at a temperature whereinthe precursor decomposes, and the nanoparticle is formed. Thenanoparticle may include a metal and a capping agent coupled to themetal. The metal may be a Group IV metal. At least one of thenanoparticles may have an average particle diameter of between about 1to about 100 angstroms. At least one of the nanoparticles may produce anelectric field in response to a stimulus. The system may include areceptor functioning to interact with the biological entity. Thereceptor may be coupled to the nanoparticle.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description as well as further objects, features andadvantages of the methods and apparatus of the present invention will bemore fully appreciated by reference to the following detaileddescription of presently preferred but nonetheless illustrativeembodiments in accordance with the present invention when taken inconjunction with the accompanying drawings.

FIG. 1 depicts a schematic flow chart of an embodiment of a batchreaction method.

FIG. 2 depicts an embodiment of the invention showing a stericallystabilized nanoparticle with attached capping ligands.

FIG. 3 depicts a schematic of an embodiment of a continuous flowproduction system.

FIG. 4 depicts an embodiment of a floating gate memory device.

FIG. 5 depicts an embodiment of a basic design for a light emittingdevice.

FIG. 6 depicts an embodiment of a basic design for a flat panel display.

FIG. 7 depicts an embodiment of a basic design for a flat panel displayincluding multiple layers of transparent light emitting devices.

FIG. 8 depicts a schematic representation of an embodiment of ananoparticle labeled analyte.

FIG. 9 depicts an embodiment of a basic design for a laser with anoptical excitation source.

FIG. 10 depicts an embodiment of a basic design for a laser using anelectrical excitation source.

FIG. 11 depicts a schematic of an embodiment of a battery based on thenanoparticles described herein.

FIG. 12 depicts an example of energy-dispersive X-ray spectroscopyanalysis of an exemplary nanoparticle composition.

FIG. 13 depicts an example of X-ray Photoelectron spectroscopy analysisof an exemplary nanoparticle composition.

FIG. 14 depicts an example of Fourier transformed infrared spectroscopyanalysis of an exemplary nanoparticle composition.

FIG. 15 depicts an example of photoluminescence (PL) andphotoluminescence excitation (PLE) spectral analysis of exemplarynanoparticle compositions.

FIG. 16 depicts an example of an absorbance profile of exemplarynanoparticle compositions.

FIG. 17 depicts a comparison between the extinction coefficients of bulksilicon as compared to the extinction coefficient of an exemplarynanoparticle composition.

FIG. 18 depicts an example of room temperature photoluminescence (PL)and photoluminescence excitation (PLE) spectra of CdS qdots.

FIG. 19 depicts an example of room temperature absorbance spectrum of anaqueous dispersion of CdS quantum dots.

FIG. 20 depicts an example of room temperature absorbance spectra of CdSqdots and CdS/antibody complexes.

FIG. 21 depicts examples of single dot PL spectra.

FIG. 22 depicts examples of X-ray Photoelectron spectroscopy (XPS) ofuncapped and capped copper nanoparticles.

FIG. 23 depicts an example of room-temperature UV-visible spectra oforganically capped copper nanoparticles.

FIG. 24 depicts an example of an atomic force microscopy (AFM) histogramshowing a silicon nanoparticle height distribution.

FIG. 25 depicts an example of room temperature absorbance, PLE and PLspectra for silicon nanoparticles.

FIG. 26 depicts an example of blinking—a comparison between the blinkingof a single dot (top) and the blinking of a cluster (bottom); insetshows a histogram of the “off” times for the single dot blinking.

FIG. 27 depicts an example of an average room temperature lifetimemeasurement of the ensemble.

FIG. 28 depicts an example of an observation of “molecular” (

) and “continuum” (----) like single nanocrystal spectra Average of 37molecular type spectra and 31 continuum type spectra from singlenanoparticles excited at 488 nm. Each spectra was shifted so that itsmaximum was at zero before averaging. Histogram insets of spectralmaxima (ëmax) of continuum type and molecular type spectra,respectively.

FIG. 29 depicts an example of a comparison of the measured ensemblespectra (

) to the reconstructed ensemble spectra. reconstructed from the singledot spectra (----) of 68 individual silicon nanoparticles.

FIG. 30 depicts a table of fluorescence lifetime measurements on Sinanoparticle dispersions. The fluorescence decay curves were fit withthree exponential functions.

FIG. 31 depicts a schematic of an experimental setup forelectrochemistry and electrogenerated chemiluminescence ofnanoparticles.

FIG. 32 depicts several examples of cyclic voltammograms anddifferential pulse voltammograms for several batches of siliconnanoparticles.

FIG. 33 depicts several examples of electrogenerated chemiluminescencetransients.

FIG. 34 depicts several examples of electrogenerated chemiluminescencespectra.

FIG. 35 depicts a schematic of an embodiment of a mechanism forelectrogenerated chemiluminescence and photoluminescence of siliconclusters and an example of a photoluminescence spectra at differentexcitation energy.

DETAILED DESCRIPTION

Nanoparticles may be prepared by using the methods described herein. Inone embodiment, nanoparticles may be formed by reacting anorganometallic precursor in the presence of a capping agent Theorganometallic precursor and capping agent may be heated at a pressuregreater than 1 atm. in a reaction vessel. The reaction vessel may bemade of type II titanium, or other titanium, stainless steel, or anyother material rated for high temperatures and high pressures. Heatingof the organometallic precursor results in the thermal degradation ofthe organometallic precursor, which in turn leads to the formation ofnanoparticles. The precursor may degrade through a free radicalmechanism, or it may degrade through thermolysis. The dimensions of thenanoparticles may be controlled by reaction conditions and the cappingagent used. The reaction conditions used to control the particle sizemay include, for example, the temperature, pressure, precursorconcentration, capping ligand concentration, solvent, precursorcomposition and capping agent composition. In one embodiment a freeradical initiator may be added to the reaction. The nanoparticle may becontrolled structure with a capping ligand or passivating ligand. It isbelieved that the capping agent may aid in controlling the dimensions ofthe formed nanoparticles by inhibiting growth of the nanoparticles. Thecapping agent may also prevent reactive degradation of the nanoparticleswhen exposed to water and oxygen and other chemical contamination.

Under the reaction conditions of high temperature and pressure, the sizeof nanoparticles may be controlled by altering the pressure,temperature, amount of precursor, amount of capping agent or by alteringa combination of conditions and reagents to produce a narrowdistribution of nanoparticle size ranges. In some embodiments,conditions may be controlled for the express purpose of producing a widedistribution of nanoparticle size ranges. It should be appreciated thatthe methods and compositions described can be modified to accommodatethe construction of nanoparticles from a variety of thermally degradableprecursors by modifying the reaction vessel, addition of a solvent,altering the capping agent, and/or reagents, or through the sequentialaddition of reactants after initial particle nucleation.

The organometallic precursor may be a Group IV metal that includesorganic groups. As used herein a “Group IV metal” includes the elementsof silicon, germanium, and tin. Generally, organometallic Group IVprecursors are compounds that may be thermally degraded to formnanoparticles that are composed primarily of the Group IV metal. In someembodiments, the nanoparticle contains a mixture of Group IV elements,such as Si_(x)Ge_(1-x), Si_(x)Sn_(1-x), or Ge_(x)Sn_(1-x).Organometallic Group IV precursors include, but are not limited toorganosilicon, organogermanium and organotin compounds. Some examples ofGroup IV precursors include, but are not limited to, alkylgermaniums,alkylsilanes, alkylstannanes, chlorosilanes, chlorogermaniums,chlorostannanes, aromaticsilanes, and aromatic germaniums andaromaticstannanes. Particular examples of organometallic siliconprecursors include, but are not limited to, tetraethyl silane ordiphenylsilane. Particular examples of organometallic germaniumprecursors include, but are not limited to, tetraethylgermane ordiphenylgermane.

The capping agent may interact with an organometallic precursor duringformation of the nanoparticle to assist in controlling the growth of theparticle. The capping agent may bond covalently to the particle surface,or stick through weak interactions, such as hydrogen bonding. Thecapping agents may physisorb to the particle surface. In one embodiment,capping of the particle surfaces may occur through a combination oforganic ligands and inorganic small molecules. Oxygen or sulfur may alsobond to the surface in some instances. Additionally, the capping agentmay assist in solubilizing the organomettalic precursor. Additionally,two or more kinds of capping agents might be added to the reactionmixture. In one embodiment, a mixture of organometallic precursors maybe added to the reactor for particle formation.

Capping agents include compounds having the general formula (R)_(n)—X,where X is an atom or functional group capable of binding to the surfaceof the nanoparticles. The term “binding” refers to an interaction thatassociates the capping agent with the nanoparticles. Such interactionsmay include ionic, covalent, dipolar, dative, quadrupolar or van derWalls interactions. Each R group is independently hydrogen, an arylgroup having between 1 and 20 carbon atoms or an alkyl group havingbetween 1 and 20 carbon atoms. X may be an atom that includes, but isnot limited to, nitrogen, carbon, oxygen, sulfur, and phosphorus.Alternatively, X may be a functional groups that includes, but is notlimited to, a carboxylate, a sulfonate, an amide, an alkene, an amine,an alcohol, a hydroxyl, a thioether, a phosphate, an alkyne, an ether,or a quaternary ammonium group. Examples of capping agents include, butare not limited to, alcohols, alkenes, alkynes, thiols, ethers,thioethers, phosphines, amines, amides, carboxylates, sulfonates, orquaternary ammonium compounds.

In some embodiments, the capping agent may be an alcohol. Alcohols thatmay be used include n-alcohols having between 1 to 20 carbon atoms. Anexample of such an n-alcohol is 1-octanol. In other embodiments, thecapping agent may be an alkene. Alkenes that may be used includealpha-olefins having between 1 to 20 carbon atoms, or olefins withunsaturated chains. An example of such an alkene is 1-octene. In anotherembodiment the capping agent may be a thiol. Thiols that may be usedinclude 1-thiols having between 1 to 20 carbon atoms. An example of sucha thiol is 1-thiooctanol.

The reaction of the organometallic precursor and the capping agents isconducted at temperature above room temperature (e.g., above about 25°C.), and at pressures above atmospheric pressure (e.g., above about 1atm.). The temperature chosen for the reaction is such that theorganometallic precursor will be thermally decomposed to produce thenanoparticles. In some embodiments, a reducing agent, such as sodiumborohydride, or lithium borohydride, or hydrogen, might be added to aidnanoparticle formation. In some embodiments, the reaction may beconducted in a pressurized reaction vessel at a temperature above theboiling point of the organometallic precursor, the capping agent, orboth the organometallic precursor and the capping agent. Thus, areaction may be at a temperature above the boiling point of one or moreof the reactants and be pressurized such that the solvent is kept in aliquid or diffusible state. The reaction mixture may be heated andpressurized above the critical point of the mixture, or it may be belowthe critical point of the mixture, either as a superheated liquid, or inthe gas-liquid two-phase region of the phase diagram. The pressure underwhich a reaction is performed may be high enough to raise the boilingpoint of a solvent but still be below the critical pressure of asolvent. The temperature and pressure may be such that the precursor andcapping ligands will be diffusible in the solvent

In other embodiments, the reaction may be conducted in a super criticalfluid. A supercritical fluid is obtained by heating a fluid above thecritical temperature and at a pressure above the critical pressure forthe fluid. The critical temperature and critical pressure for a fluid isknown as the critical point. Above the critical point neither a liquidnor gas state exist. Instead a phase known as a supercritical fluidexists. For example, a gas enters the supercritical state when thecombination of pressure and temperature of the environment in which thegas is contained is above a critical state. The critical temperature ofoctanol is 385° C. The critical pressure of octanol is 34.5 bar. Whenoctanol is subjected to temperatures and pressures above 385° C. and34.5 bar, the octanol exists in a supercritical state. The criticaltemperature and pressure of other components may be readily calculatedor experimentally determined. The particle size may be controlled byvarying the pressure of the reaction mixture under isothermal conditionsabove or below the critical point of the mixture. The particle size maybe controlled by varying the temperature of the reaction mixture underisobaric reaction conditions above or below the critical point of themixture.

A compound or element above the critical temperature and criticalpressure is referred to as a supercritical fluid. Supercritical fluidsmay have high solvating capabilities that are typically associated withcompositions in the liquid state. Supercritical fluids also have a lowviscosity that is characteristic of compositions in the gaseous state.Additionally, a supercritical fluid maintains a liquid's ability todissolve substances.

Many organometallic Group IV metal precursors require high temperatures(above about 300° C.) to induce the decomposition into nanoparticles.The high temperatures needed to decompose the organometallic precursorstypically exceed the boiling points of the capping agent, the solvent,and the precursor itself. The use of elevated pressure or super criticalconditions allows the decomposition of organometallic precursors to formnanoparticles using the capping agents described above. In oneembodiment, the high temperatures are necessary to drive the reactionbetween the nanoparticle surface and the capping agents. In anotherembodiment, the capping agent may react spontaneously upon nanoparticleformation.

In some embodiments, the reaction may be conducted at a temperature andpressure that is above the critical point of the capping agent. Thecapping agent may, therefore, become a supercritical fluid. This allowsthe reaction to be conducted at a temperature that induces decompositionof the organometallic precursor and reaction of the capping agent withthe forming nanoparticle. Additionally, the supercritical fluid maypromote rapid reactant diffusion. Rapid diffusion of the reactants mayallow diffusion-limited growth which may lead to narrow particle sizedistributions. Particles may also grow through a coagulative growthprocess to yield stable redispersible nanoparticles.

In another embodiment, the decomposition of the organometallic precursormay be conducted in the presence of a capping agent and a substantiallyinert solvent. Generally, a solvent will dissolve both precursormolecules and capping agents. Examples of solvents that may be usedinclude, but are not limited to, hydrocarbons, alcohols, ketones, ethersand polar aprotic solvents (e.g., dimethyl formamide, dimethylsulfoxide, etc). Hydrocarbon solvents include, but are not limited toaromatic and non-aromatic hydrocarbon carbons. Examples of aromatichydrocarbon solvents include, but are not limited to benzene, toluene,and xylenes. Examples of non-aromatic hydrocarbon solvents includecyclic hydrocarbons (e.g., cyclohexane, cyclopentane, etc.) andaliphatic hydrocarbons (e.g., hexane, heptane, octane, etc.). In certainembodiments the reaction may be performed at conditions, such astemperature and pressure, which are below the critical point of solvent,but above the boiling point of the solvent. Thus, a reaction may be at atemperature above its ambient boiling point and be pressurized such thatthe boiling point is elevated above the temperature of the reactionconditions, thus maintaining the solvent in a liquid or diffusiblestate. The pressure under which a reaction is performed may be highenough to raise the boiling point of a solvent but still be below thecritical pressure of a solvent. The temperature and pressure may be suchthat the precursor and capping ligands will be diffusible in the solvent

In other embodiments the solvent may be at supercritical conditions. Thetemperature and pressure may be such that the precursor and cappingagents will be diffusible in the solvent. Thus, reaction condition maybe above and below the critical point of a solvent.

The temperatures at which the reactions are carried out are sufficientfor the thermal degradation of the precursor molecules. The temperatureof the reaction will vary with the characteristics of the precursormolecules. In certain embodiments the temperature may be in theapproximate range of 300° C. to 800° C., in some embodiments 400° C. to700° C. and the temperature can be approximately 450° C. to 550° C. Inan embodiment the reaction may be approximately 500° C.

The pressure at which the reaction is carried out should be sufficientto maintain at least a portion of the precursor and at least a portionof the capping ligand in a diffusible state and/or a solvent in a denseliquid or gaseous state with a solvent density above 0.1 g/mL. Incertain embodiments the reaction conditions may be beyond the criticalpoint of a solvent and/or capping agent. For example, it is envisionedthat supercritical octanol can be used as a capping agent. In certainembodiments pressures of approximately 2 to 500 bar may be used. Inother embodiments the approximate range of pressure may be 25 to 400bar. In certain embodiments approximately 50-350 bar is preferred.

When a solvent is used the organometallic precursor may be present inthe initial reaction solution at various concentrations ranging fromnanomolar to micromolar to molar concentrations. In certain embodimentsa precursor may be present in the approximate range of 10 mM to 5 M, 125to 625 mM, 250 to 500 mM, 300 to 500 mM, or 400 mM to 1 M. Additionally,the mole ratio of capping agent to the organometallic precursor may bein the approximate range of 1,000,000:1 to 1:1,000 when a solvent isused. In other embodiments the ratio may be in the approximate range of10,000:1 to 1:10,000. In other embodiments the mole ratio of reagentsmay be in an approximate range from 1 to 1,000,000 parts capping agentto 1 to 10 parts precursor molecule, or in the approximate range of 500to 50,000 parts capping agent to 1 to 10 parts precursor molecule, or inthe approximate range of 800 to 10,000 parts capping agent to 1 to 10parts precursor molecule.

Nanoparticles may be produced using a batch process, a semibatch processor a continuous flow process. FIG. 1 illustrates an embodiment of anapparatus for producing nanoparticles using a batch process. Reactionvessel 2 may be in fluid communication with high-pressure pump 4.Reaction vessel 2 may be a stainless steel cell (High Pressure Equip.Co., Buffalo, N.Y.), or an inconnel high pressure cell, or a titaniumcell. Alternative high-pressure vessels may be used to carry out themethods of the invention. Alternatives include, but are not limited to,iron based alloys and titanium alloys. Reaction vessel 2 may beoperatively coupled to thermal source 6 and thermometer 8. Reagents arepumped into reaction vessel 2 from a reagent reservoir 10. Reagentreservoir 10 may include the solvent, precursor, and capping agent. Oncethe reagents are pumped into reaction vessel 2 reaction vessel 2 may bepressurized and heated to the appropriate temperature and pressure.After allowing sufficient time for the thermal degradation of aprecursor molecule and the subsequent formation of nanoparticles thereaction may be cooled and brought to ambient pressures. The reactionmay occur in a matter of seconds, or in some embodiments, the reactionoccurs in a matter of several hours. The reaction time, or the residencetime in the reactor may dictate the particle size, with longer residencetimes leading to larger particle sizes. The product is removed from thevessel 2 for further processing. The product may then be sprayed,purified, extracted, and/or size fractionated.

Products may be isolated and dried to remove the solvents and/orvolatile reaction products. The dried products may then be redispersedin an appropriate solvent, such as chloroform or hexane. Alternativesolvents for redispersion include but are not limited to hydrocarbons,ethers, alcohols, ketones, and compressed fluids such as ethane, propaneor carbon dioxide. In particular embodiments the capping agents may betailored for redispersion in water, carbon dioxide, fluorocarbons, andother organic and polar solvents.

After the reaction is at least partially completed, the reaction vesselmay include a mixture of nanoparticles and unreacted organometallicprecursors. If no solvent is used, the nanoparticles may be dissolved orsuspended in the capping agent If a solvent is used, the nanoparticlesmay be dissolved or suspended in the solvent. The size distribution ofthe nanoparticles is typically determined by the reaction conditions andreagents. To narrow the size distribution of particles variousseparation techniques may be used. The nanoparticles may be separatedfrom the unreacted reagents by a variety of techniques.

In an embodiment, the nanoparticles may be isolated from the reactioncompartment by flushing with a solvent. The solvent may be an organicsolvent, or a polar solvent, depending on the nanoparticle solubility.The reactor may be flushed once, or several times, to remove thenanoparticle. Because nanoparticles have an average diameter of lessthan about 100 nm, the addition of a solvent causes the particles tobecome “dispersed” within the solvent. When dispersed in a solvent, thenanoparticles may exist as individual particles that are separated formother nanoparticles by the solvent. Particles may be removed from thesolvent by treating with a second solvent. The second solvent may induceaggregation of the nanoparticles. Aggregation of the nanoparticle maycause particles to associate with each other to form aggregates ofparticles. These aggregates may be filtered to remove the solvent andother impurities in the reaction mixture.

During formation of nanoparticles, a nanoparticles having a largeaverage particle size distribution may be obtained. In some embodiments,the size distribution of particles may be narrowed by the choice ofsolvents used for the isolation process. As described above,nanoparticles may be dispersed in a solvent. The addition of a secondsolvent may induce aggregation of the nanoparticles. In someembodiments, the second solvent may induce only a portion of thenanoparticle having a narrow particle size distribution to be isolated.For example, if the nanoparticles formed after reaction of theorganometallic precursor have a average particle size ranging from 1 toabout 100 nm, the addition of a second solvent may induce aggregation ofonly nanoparticles in the 2540 nm range. In this example, nanoparticleshaving an average particle size greater than 40 nm or less than 25 nm donot aggregate and remain dispersed in the solvents. The aggregatedparticles may be removed by filtration. By varying the solvent used, thesize of the nanoparticles that aggregate may be altered allowing easyisolation of nanoparticles having a specific particle size distribution.Aggregated nanoparticles may be collected through centrifugation,filtering, or other means of collecting a solid from a slurry. Selectiveextraction may be carried out using polar/nonpolar miscible solventpairs, including, but not limited to, chloroform/ethanol, orhexane/ethanol, or water/ethanol.

In other embodiments chromatography may be used to size fractionatenanoparticles of the present invention. Chromatography methods may beused to separate nanoparticles based on size, shape, charge,hydrophobicity, or other characteristics that distinguish thenanoparticles. In some embodiments liquid chromatography may be used.The liquid chromatography may be conducted at ambient pressures or athigh pressures using high pressure liquid chromatography (HPLC). Thecolumn may be packed with size exclusion gel that separates smallunreacted byproducts from the larger particles. In other embodiments,the column may consist of, but is not limited to, an ion exchange resin,a reverse chromatography packing, or silica. Any suitable size-exclusionor reverse-phase chromatographic packing may be used for the separation.In one embodiment, Bio-Beads™, (Bio-Rad, Hercules, Calif.) may be used.

In another embodiment, a flow process may be used for the manufacture ofnanoparticles. A flow process offers a way to produce nanoparticlescontinuously. FIG. 3 depicts a schematic of an embodiment of acontinuous flow production system. In an embodiment, continuous flowsystem 16 may include reactor 18, a first heater 19 coupled to reactor18, a temperature monitor 20 coupled to reactor 18, and injector 22coupled to reactor 18. Reactor 18 may include inlet 24 and outlet 26.First heater 19 may function to control the temperature of the reactorduring use. Temperature monitor 20 may function to monitor the reactiontemperature during use. Injector 22 may function to inject the reagentsinto the reactor 18 at pressure greater than 1 atm.

In certain embodiments, reactor 18 may be a high-pressure reactionvessel. Certain embodiments use a stainless steel cell (High PressureEquip. Co., Buffalo, N.Y.), or an inconnel high pressure cell.Alternative high-pressure vessels may be used to carry out the methodsof the invention. Alternatives include, but are not limited to, ironbased alloys and titanium. First heater 19 may be used to control thetemperature of reactor 18. In one embodiment, a first heater may be aheating tape. Other types of heaters include, but are not limited toheating mantles, oil baths, metal baths, resistive heaters, and hot airheaters.

In an embodiment, reactor 18 may be of a length such that precursorsdecompose to form nanoparticles during the time the precursors are inreactor 18. The flow rate of the precursors and capping agents may beadjusted to ensure the reaction runs to completion.

Temperature monitor 20 may be coupled to reactor 18 and include a devicefor observing the temperature of the reaction within reactor 18. Thetemperature monitor should also be capable of withstanding thepotentially harsh conditions therein. A non-limiting example of atemperature monitor is a platinum resistance thermometer.

In an embodiment, continuous flow system 16 may also include mixingchamber 28. Mixing chamber 28 may be coupled to inlet 24 and may includesecond heater 29 functioning to preheat precursor, capping agent, andsolvent before injecting the mixture into reactor 18. Injector 22 may becoupled to mixing chamber 28 and function to inject the solvent intomixing chamber 28 at the appropriate pressure. Mixing chamber 28 mayinclude a second heater which may function to control the temperature ofmixing chamber 28. One skilled in the art may envision numerous means ofcontrolling the temperature of mixing chamber 28 known to the art.

Continuous flow system 16 may include injector 22. In some embodiments,injector 22 may be coupled to reactor 18, in other embodiments injector22 may be coupled to mixing chamber 28, or in other embodiments injector22 may be coupled to mixing chamber 28 and reactor 18. When injector 22is coupled to mixing chamber 28 and reactor 18 there may exist a systemfor controlling the flow from injector 22 to mixing chamber 28 andreactor 18. Injector 22 may function to transfer a solvent over a rangeof pressures necessary to solvate the nanoparticles precursors and thecapping agent. Injector 22 may include tube 30 and pump 32. Tube 30 mayinclude a moveable member or piston 34 positionable within tube 30 andadapted to inhibit material from moving within tube 30 from one side ofpiston 34 to another side of piston 34. Pump 32 may function to transfermaterial including a fluid or a gas in an end of tube 30 on one side ofpiston 34. The fluid or gas may exert a force on positionable piston 34,moving piston 34 and subsequently exerting a force on a solvent locatedin tube 30 on an opposite side of piston 34.

In some embodiments, continuous flow system 16 may be sealed fromoutside contamination and under an inert atmosphere. Use of an inertatmosphere may reduce the extent of incidental oxidation of the surfaceof the crystalline composition.

FIG. 2 illustrates an example of sterically stabilized nanoparticles 12.Shown in FIG. 2 are capping agents 14 coupled to the nanoparticles.Capping agents 14 may be flexible organic molecules, alkanes are anon-limiting example, that typically provide repulsive interactionsbetween nanoparticles 12 in solution. The repulsive nature of cappingagents 14 typically prevents uncontrolled growth and aggregation ofnanoparticle 12. Generally, the core of nanoparticle 12 tends to be welldefined and faceted. However, in other embodiments, the particles may bespherical or ellipsoidal. In one embodiment, the nanoparticle core maybe amorphous.

Nanoparticles produced using the method described herein may bestructurally, chemically, and optically characterized. For example,nanoparticles may be characterized by transmission electron microscopy(EM), energy-dispersive X-ray spectroscopy (EDS), Fourier transforminfrared spectroscopy (FTIR), UV-visible absorbance, and luminescence(both PL and PLE) spectroscopy data. In certain embodiments,nanoparticles may be crystalline cores coated by hydrocarbon ligandsbound through covalent alkoxide bonds or interactions of a thiol groupwith the nanoparticle surface. In other embodiments the nanoparticlecores may be bonded covalently through an Si—C linkage. Thenanoparticles may have residual oxygen, or sulfur on their surfaces. Thenanoparticles typically luminesce with size-tunable color, from the blue(approximately 15 Å diameter for silicon nanoparticles) to green(approximately 25 to 40 Å diameter for silicon nanoparticles) into theyellow, orange and red for particles that can be in up to 80 Å indiameter. The nanoparticles may exhibit charge transfer betweenneighboring particles. Typically, the emission color depends also on theexcitation energy, either by photo or electrical means.

In one embodiment, nanoparticles may be stimulated so as to emit light.Discrete optical transitions also may appear in the absorbance andphotoluminescence excitation (PLE) spectra of the nanoparticles, whichis generally consistent with quantum confinement effects insemiconductors. The particle distribution is typically within a standarddeviation about the mean particle diameter. The appearance of discreteoptical transitions, or peaks, in the absorbance and/or luminescencespectra typically indicates a narrow size distribution, as the opticalproperties of the nanoparticles themselves are size-dependent.Furthermore, the appearance of discrete peaks typically indicates thehomogeneous chemical nature of nanoparticles, including core chemistry,crystallinity, surface chemistry and chemical coverage. In certainembodiments particle size distribution may affect the appearance ofdiscrete transitions in the optical spectra Typically in these smallparticles, the energy levels have separated significantly compared tobulk silicon, making these transitions observable, an effect of quantumconfinement. In certain embodiments particle surface chemistry mayaffect the appearance of discrete transitions in the optical spectra andmay broaden the PL emission energies.

In some embodiments, nanoparticles may exhibit previously unobserveddiscrete electronic absorption and luminescence transitions due toquantum confinement effects. Nanoparticles described herein may exhibitdiscrete electronic absorption and luminescence transitions due toquantum confinement effects that are dependent upon the size of thenanoparticles. Differences in the discrete optical properties due todifferences in the size of the nanoparticles may translate intodifferently sized nanoparticles emitting light at different wavelengthsand colors. Several non limiting examples include: silicon nanoparticleswith an average diameter of about 2 nm emitting a blue light; siliconnanoparticles with an average diameter of about 3.5 nm emitting a greenlight; silicon nanoparticles with an average diameter of about 4.5 nmemitting a yellow light; silicon nanoparticles with an average diameterof about 6 nm emitting an orange light; and silicon nanoparticles withan average diameter of about 7-8 nm emitting a red light. In certainembodiments, the surface chemistry may shift the emission energies toslightly lower values. For example, 2 nm silicon nanoparticles may emitgreen light, or even in the case of very heavy surface oxidation, forexample, although the surface coating is not limited to oxygen, theseparticles may emit orange or red light. Studies confirm that siliconclusters as small as 15 Å may behave as indirect semiconductors. Themethod for nanoparticle formation may be applied to other materials,such as nanowires, that typically require temperatures greater than theboiling point of available solvents under ambient pressure, typicallygreater than 350° C., for crystal formation. Absorbance of thecompositions may range from approximately 1000 nm to approximately 350nm. In particular embodiments, the compositions may be excitedelectronically. The compositions may display photoluminescence at 300 nmto 1000 nm. Generally, photoluminescence decays by less than 50% whenexposed to the atmosphere for 30 days. In particular embodiments of theinvention the size of nanoparticles typically produced are in theapproximate range of 10 Å to 200 Å and larger. In other embodiments thesize of the nanoparticles typically produced are in the approximaterange of 15 to 40 Å. Size distributions that display discrete opticaltransitions typically are 15 to 25 Å and may be luminescent at 350 to500 nm.

In some embodiments, nanoparticles may exhibit shorter photoluminescencelifetimes than those previously observed for the same element Forexample, porous silicon and oxide capped silicon nanoparticles havepreviously exhibited microsecond scale photoluminescence lifetimes.Examples of silicon nanoparticles formed by methods described hereinexhibit a photoluminescence lifetime (greater than 96% of the totalphotoluminescence lifetimes) of less than or equal to 20 ns. An exampleof an octanethiol-capped silicon nanoparticles exhibits characteristiclifetimes with a fast component (˜100 picoseconds) and two slowcomponents with lifetimes ranging from 2 to 6 as. The slow componentsphotoluminescence lifetimes observed for the octanethiol-capped siliconnanoparticles example are at least three orders of magnitude faster thanthose previously found for porous silicon and silicon nanoparticles. Themeasured lifetime relates to the radiative and non-radiativeelectron-hole recombination processes. Faster electron-holerecombination processes may be better for certain applications such aslight emitting devices or light emitting diodes (LEDs) and opticalswitches. Coating the nanoparticles with a different wider band gapsemiconductor, such as CdS or ZnS, may reduce the non-radiative rates.Coating the nanoparticles with a smaller band gap semiconductor like Gemay increase the photolurninescence lifetime in the particles. Forcertain applications, the photoluminescence lifetime may be increasedthrough the use of different capping ligands.

Nanoparticles described herein may be relatively stable when chargingthe nanoparticles with electrons or electron holes. Stability of thenanoparticles during charging with electrons and electron holes may makethe nanoparticles suitable for floating gate memory. In anotherembodiment, stability of the nanoparticles during charging may makethese materials suitable for photocatalytic or battery applications.

Nanoparticles described herein may exhibit quantized, or discrete,charging. Quantized charging may allow for use of the nanoparticles inmulti-valued logic applications. The nanoparticles may exhibitreversible multiple charge transfers. Reversible charge transferring ofnanoparticles may allow for light emission by charge injection, orelectrogenerated chemiluminescence. The nanoparticles may emit lightunder repetitive electrode potential cycling or pulsing betweennanoparticles oxidation and reduction. In electrogeneratedchemiluminescence experiments, electron transfer annihilation ofelectrogenerated anion and cation radicals results in the production ofexcited states:R⁻+R⁺→R*+R  (1)R*→R+hv  (2)In this case, R⁻ and R⁺ refer to negatively and positively chargedsilicon nanoparticles electrogenerated at an electrode (for example,Pt), which then react in solution to give the excited state R* asillustrated in reaction 1 and 2 herein. This property may form the basisfor sensor technologies.

Nanoparticles of other metals may be formed by heating organometallicprecursors in the presence of a capping agent. For example, Group II-VIand Group III-V nanoparticles may also be prepared by using methodssimilar to those described above for Group IV metals. Additionally,nanoparticles of Group II, Group III, Group V, and Group VI metals maybe formed using methods similar to those described above for the GroupIV metals. In one embodiment, nanoparticles may be formed by reactingone or more organometallic precursors in the presence of a cappingagent. The organometallic precursors and capping agent may be heated ata pressure greater than 1 atm. in a reaction vessel. Heating of theorganometallic precursors results in the thermal degradation of theorganometallic precursor, which in turn leads to the formation ofnanoparticles. The precursors may degrade through a free radicalmechanism, or it may degrade through thermolysis. The dimensions of thenanoparticles may be controlled by reaction conditions and the cappingagent used. The reaction conditions used to control the particle sizemay include, for example, the temperature, pressure, precursorconcentration, capping ligand concentration, solvent, precursorcomposition and capping agent composition. In one embodiment a freeradical initiator may be added to the reaction. It is believed that thecapping agent may aid in controlling the dimensions of the formednanoparticles by inhibiting growth of the nanoparticles. The cappingagent may also prevent reactive degradation of the nanoparticles whenexposed to water and oxygen and other chemical contamination.

A Group II organometallic precursor may be a Group II metal thatincludes organic groups. As used herein a “Group II metal” includes theelements of zinc, cadmium, and mercury. Group II organometallicprecursors include, but are not limited to organozinc, organocadmium andorganomercury compounds. Some examples of Group II organometallicprecursors include, but are not limited to, alkylzincs, alkylcadmiums,alkylmercurys, arylzincs, arylcadmium and arylmercury. Examples oforganometallic zinc precursors include, but are not limited to, dimethylzinc, diethyl zinc, and diphenyl zinc. Examples of organometalliccadmium precursors include, but are not limited to, dimethyl cadmium,diethyl cadmium, and diphenyl cadmium. Examples of organometallicmercury precursors include, but are not limited to, dimethyl mercury,diethyl mercury, and diphenyl mercury. Organometallic zinc andorganometallic mercury precursors may be formed by the reaction ofmetallic mercury or zinc with an alkyl or aryl halide by known methods.Organometallic cadmium precursors may be formed by the reaction ofcadmium halides with Grignard reagents (e.g., RMgX) by known methods.

A Group VI organometallic precursor may be a Group VI metal thatincludes organic groups. As used herein a “Group VI metal” includes theelements of selenium tellurium. Group VI organometallic precursorsinclude, but are not limited to organoselenides, organotellurides. Someexamples of Group VI precursors include, but are not limited to,dialkylselenides, dialkyltellurides, diarylselenides, diaryltellurides,dialkyldiselenides, dialkylditellurides, diaryldiselenides,diarylditellurides. Examples of organometallic selenium precursorsinclude, but are not limited to, dimethylselenide, diethylselenide,diphenylselenide, dimethyldiselenide, diethyldiselenide, anddiphenyldiselenide. Examples of organometallic tellurium precursorsinclude, but are not limited to, dimethyltelluride, diethyltelluride,diphenyltelluride, dimethylditelluride, diethylditelluride, anddiphenylditelluride. Organometallic selenium and tellurium precursorsmay be formed by the reaction of sodium selenide or sodium telluridewith alkyl or aryl halides by known methods.

A Group III organometallic precursor may be a Group III metal thatincludes organic groups. As used herein a “Group III metal” includes theelements of boron, aluminum, gallium, indium, and thallium. Group IIIorganometallic precursors include, but are not limited to organogalliumcompounds, organoindium compounds, and organothallium compounds. Someexamples of Group III precursors include, but are not limited to,trialkylgallium compounds, trialkylindium compounds, trialkylthalliumcompounds, triarylgallium compounds, triarylindium compounds,triarylthallium compounds. Examples of organometallic gallium precursorsinclude, but are not limited to, trimethylgallium and triphenylgallium.Examples of organometallic thallium precursors include, but are notlimited to, trimethylthallium and triphenylthallium. Examples oforganometallic indium precursors include, but are not limited to,trimethylindium and triphenylindium. Organometallic gallium, indium, andthallium precursors may be formed by the reaction of the appropriatemetal halide (e.g., GaCl₃, InCl₃, or TlCl₃) with Grignard reagents(e.g., RMgX) or trialkyl- or triaryl aluminum compounds by knownmethods.

A Group V organometallic precursor may be a Group V metal that includesorganic groups. As used herein a “Group V metal” includes the elementsof phosphorus, arsenic, and antimony. Group V organometallic precursorsinclude, but are not limited to organophosphorus compounds,organoarsenic compounds, and organoantimony compounds. Some examples ofGroup III precursors include, but are not limited to, trialkylphosphoruscompounds, trialkylarsenic compounds, trialkylantimiony compounds,triarylphosphorus compounds, triarylarsenic compounds, triarylantimonycompounds. Examples of organometallic phosphorus precursors include, butare not limited to, trimethylphosphine and triphenylphosphine. Examplesof organometallic arsenic precursors include, but are not limited to,trimethylarsenide and triphenylarsenide. Examples of organometallicantimony precursors include, but are not limited to, trimethylantimonyand triphenylantimony. Organometallic phosphorus compounds arecommercially available. Organometallic gallium, indium, and thalliumprecursors may be formed by the reaction of the appropriate metal halide(e.g., GaCl₃, InCl₃, or TiCl₃) with Grignard reagents (e.g., RMgX) ortrialkyl- or triaryl aluminum compounds by known methods.

Nanoparticles may be formed by taking one or more of the Group II, III,IV, V, or VI organometallic precursors and heating them in the presenceof a capping agent. In one embodiment, the organometallic precursor andthe capping agent may be reacted at supercritical conditions. Thereaction may be conducted at or above the critical point of the cappingagent. Alternatively, a solvent may be used. The reaction may beconducted above the critical point of the solvent, the capping agent, orboth the solvent and the capping agent. The solvent and capping agentare as defined previously.

Nanoparticles of any of the Group II, III, V, V or VI may be formed asdescribed above. In another embodiment, nanoparticles composed ofmixtures of Group II, III, IV, V, and VI. Mixtures include mixtureswithin a group and mixtures between groups. Mixtures within in a groupmay be formed by heating two or more organometallic precursors of thesame group in the presence of a capping agent. For example,silicon-germanium nanoparticles may be formed by heating a mixture of asilicon organometallic precursor (e.g., diphenylsilane) and a germaniumorganometallic precursor (e.g., diphenylgermane), a capping agent, and,optionally, a solvent. In one embodiment, the reaction is conducted atsupercritical conditions. The decomposition of the organometallicprecursors may lead to formation of silicon-germanium nanoparticles.

In another embodiment, nanoparticles that include mixtures of elementsfrom different groups may be formed. One common group of semiconductormaterials are the Group II-VI semiconductors. These materials aretypically composed of mixtures of Group II metals and Group VI metals.Group II-VI nanoparticles may be formed by heating a mixture of one ormore Group II organometallic precursors, one or more Group VIorganometallic precursors, a capping agent, and, optionally, a solventDecomposition of the organometallic precursors may lead to Group II-VInanoparticles. In one embodiment, the reaction is conducted atsupercritical conditions. For example, cadmium-selenide nanoparticlesmay be produced by heating a mixture of a cadmium organometallicprecursor (e.g., dimethyl cadmium) and a selenium organometallicprecursor (e.g., diphenyldiselenide) in the presence of a capping agent.

Group III-V nanoparticles may be formed by heating a mixture of one ormore Group III organometallic precursors, one or more Group Vorganometallic precursors, a capping agent, and, optionally, a solvent.Decomposition of the organometallic precursors may lead to Group III-Vnanoparticles. In one embodiment, the reaction is conducted atsupercritical conditions. For example, gallium-arsenide nanoparticlesmay be produced by heating a mixture of a gallium organometallicprecursor (e.g., trimethyl gallium) and an arsenic organometallicprecursor (e.g., trimethyl arsenide) in the presence of a capping agent.In another example, Indium-gallium-arsenide nanoparticles may be formedby heating a mixture of a gallium organometallic precursor (e.g.,trimethyl gallium). an arsenic organometallic precursor (e.g., trimethylarsenide) and an indium organometallic precursor (e.g., trimethylindium) in the presence of a capping agent. Other materials that may beformed include, but are not limited to, indium-phosphide,indium-aresenide, and gallium-phosphide.

Group IV-V nanoparticles may be formed by heating a mixture of one ormore Group IV organometallic precursors, one or more Group Vorganometallic precursors, a capping agent, and, optionally, a solvent.Decomposition of the organometallic precursors may lead to Group IV-Vnanoparticles. In one embodiment, the reaction is conducted atsupercritical conditions. For example, phosphorus doped siliconnanoparticles may be produced by heating a mixture of a siliconorganometallic precursor (e.g., diphenylsilane) and a phosphorusorganometallic precursor (e.g., triphenyl phosphine) in the presence ofa capping agent.

Group IV-III nanoparticles may be formed by heating a mixture of one ormore Group IV organometallic precursors, one or more Group IIIorganometallic precursors, a capping agent, and, optionally, a solventDecomposition of the organometallic precursors may lead to Group IV-IIInanoparticles. In one embodiment, the reaction is conducted atsupercritical conditions. For example, boron doped silicon nanoparticlesmay be produced by heating a mixture of a silicon organometallicprecursor (e.g., diphenylsilane) and a boron organometallic precursor(e.g., triphenylborane) in the presence of a capping agent.

Group IV nanoparticles that are doped with rare earth elements may alsobe formed by heating one or more Group IV organometallic precursors, oneor more rare earth elements, a capping agent, and, optionally, asolvent. Decomposition of the organometallic precursors may lead toGroup IV nanoparticles that are doped with one or more rare earthelements. In one embodiment, the reaction is conducted at supercriticalconditions. Rare earth elements include lanthanum, cerium, praseodymium,neodymium, promethium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Forexample, ytterbium doped silicon nanoparticles may be produced byheating a mixture of a silicon organometallic precursor (e.g.,diphenylsilane) and an ytterbium precursor in the presence of a cappingagent.

Other metal precursors of other metal groups (including the transitionalmetals) may be heated to form nanoparticles. Many complexes of metalswith small organic molecules and carbon monoxide may be formed. Forexamples, many metals may form complexes with one or morecycopentadienes to form metallocenes. Many metallocenes exhibit somesolubility in organic solvents. Metallocenes may be decomposed byheating to high temperatures. When heated to high temperatures in thepresence of a capping agent, and, optionally a solvent nanoparticles maybe formed. In some embodiments, the reaction is conducted above thesupercritical point of the capping agent and/or solvent. Examples ofmetallocenes include, but are not limited to, ferrocene, cobaltocene,nickelocene, titanocene dichloride, zirconocene dichloride, anduranocene. When decomposed these metallocenes may lead to iron, cobalt,nickel, titanium, zirconium, or uranium nanoparticles respectively. Theformation of metal nanoparticles may be aided by the addition of areducing agent Reducing agents include, but are not limited to, hydrogenand hydride compounds. Hydride compounds include, but are not limitedto, lithium aluminum hydride, lithium borohydride, and sodiumborohydride.

Metal salts may also be used as precursors for the formation of metalnanoparticles and/or metal oxide nanoparticles. In one embodiment, metalsalts (e.g., metal nitrates and metal acetates) may be hydrolyzed insupercritical water to form nanoparticles of the metal or metal oxidenanoparticles. Capping agents may be used to control whether a metalnanoparticle or a metal oxide particle may be formed. For example,copper nitrate may be decomposed in supercritical water to form copper(I) oxide nanoparticles in the absence of a capping agent. When acapping agent (e.g., 1-hexanethiol) is added to copper nitrate insupercritical water the predominant product is a copper nanoparticle.Additionally, the addition of an oxidant or reducing agent may influencethe products produced. Other factors, including but not limited to,precursor concentration, solution pH, and capping ligand may affect thecrystal structure, size, morphology, and degree of agglomeration of thenanoparticles. Metal alloy nanoparticles may be made by hydrolyzingmixtures of metal salts.

Nanoparticles may be modified by further treatment after they have beenformed. For example, silicon or germanium nanoparticles may be modifiedafter synthesis using standard ion implantation techniques or iondiffusion techniques. For example, silicon nanoparticles may be doped byion implantation of phosphorus to form n-type semiconductor materials.

Additionally, nanoparticles may be further modified by additional growthafter synthesis. For example, after formation of a nanoparticle, acoating layer having the same composition or a different composition maybe formed on the nanoparticle. The coating composition may be formed byplacing the nanoparticles in the presence of a coating precursor. Thecoating precursor may be an organometallic precursor. Upon decompositionof the organometallic precursor, the material may form a coating on thenanoparticle. Growth of the coating may be regulating by the presence ofcapping agents, as described above. For example, germanium nanoparticlesmay be coated with a silicon coating layer. The silicon coating layermay be grown on the germanium nanoparticle using standard depositiontechniques. Alternatively, the silicon may be grown on the germaniumnanoparticle by placing the nanoparticle in a reactor and treating theparticle with an organometallic silicon precursor. Upon decomposition ofthe organometallic silicon precursor, silicon may form a coating on thegermanium particle. The thickness of the coating may be controlled bythe reaction conditions used and the nature of the capping agent

Applications:

Floating Gate Memory

In some embodiments, nanoparticles may be used in floating gate or flashmemory applications. Non-volatile memory such as electricallyprogrammable read-only memory (EPROM) and electrically-erasableprogrammable read-only memory (EEPROM) are used for storing data incomputer systems. EPROM and EEPROM memory includes a plurality of memorycells having electrically isolated gates, referred to as floating gates.Data is stored in the memory cells in the form of a charge on thefloating gates. Charge is transported to or removed from the floatinggates by program and erase operations, respectively.

Another type of non-volatile memory is flash memory. Flash memory is aderivative of EPROM and EEPROM. Although flash memory shares manycharacteristics with EPROM and EEPROM, the current generation of flashmemory differs in that erase operations are done in blocks.

A typical flash memory includes a memory array composed of a pluralityof memory cells arranged in row and column fashion. Each of the memorycells includes a floating gate field-effect transistor capable ofholding a charge. The cells are usually grouped into blocks. Each of thecells within a block may be electrically programmed in a random basis bycharging the floating gate. The charge may be removed from the floatinggate by a block erase operation. The charge may be negative or positive.The data in a cell is determined by the presence or absence of thecharge in the floating gate.

Flash memories have the potential of replacing hard storage disk drivesin computer systems. The advantages would be replacing a complex anddelicate mechanical system with a rugged and easily portable smallsolid-state non-volatile memory system. There are also the possibilitiesthat flash memories might be used to replace DRAMs. Flash memories havevery high potential densities and more speed of operation, particularityin the erase operation, than DRAMS. Flash memories might then have theability to fill all memory needs in future computer systems.

FIG. 4 depicts an embodiment of a floating gate field effect transistoror floating gate memory device 36. Floating gate memory device 36 mayinclude source 38, drain 40, control gate 42, and floating gate 44.Source 38 may be formed from an N+ type of high impurity concentration.Drain 40 may be formed from an N+ type of high impurity concentration.Source 38 and drain 40 may be formed in substrate 46. Substrate 46 maybe formed of a P-type semiconductor of low impurity concentration.

In some embodiments, source 38 and drain 40 may be separated from oneanother by a channel 48. Channel 48 may function as a conduit forelectron flow. In one embodiment, the channel will be a Group IVnanowire. Floating gate 44 may be positioned between channel 48 andcontrol gate 42. Floating gate 44 may be electrically isolated. Data canbe written into floating gate memory device 36 by injecting electronsthrough channel 48 or substrate 46 into floating gate 44. Reversing theflow of electrons sends electrons out of floating gate 44 erasing thestored data. Writing data to non-volatile memory may functiondifferently beginning by setting up an electric field across barrierlayer 50 to attract electrons in channel 48. In another embodiment,energy may be supplied to the electrons to overcome the barrier 50.Either method may increase the threshold voltage of the floating gatememory device 36. Variation of the threshold voltage caused by thechange in stored electric charges within floating gate 44 can representdifferent logic states, non limiting examples are ‘0’ and ‘1’. To erasestored data in a non-volatile memory device a high electric field may beset up between Source 38 and control gate 42. Consequently, electronstrapped in floating gate 44 can now penetrate neighboring barrier layer50 causing the threshold voltage to drop. This change in the thresholdvoltage may represent another logic state.

In some embodiments, floating gate 44 may include the nanoparticlesdescribed herein. The nanoparticles may be used as discretenanoparticles. In another embodiment the nanoparticles may bespin-coated as a thin film to form floating gate 44. In anotherembodiment the nanoparticles may be drop cast as a thin film to formfloating gate 44. In one embodiment, an oxide, or other dielectricmaterial may be grown over the particles. In another embodiment, aninsulating polymer or other organic molecular material might be laid ontop of the particles forming the floating gate 44. The nanoparticles mayexhibit quantized charging. Quantized charging means that electroninjection may occur as discrete charging events with discrete thresholdvoltages. Quantized charging may allow for use of the nanoparticles inmulti-valued logic applications. The nanoparticles may exhibitreversible multiple charge transfers. Traditional memory units only havetwo different logic states usually represented as ‘0’ and ‘1’. Memorydevices including nanoparticles described herein may be capable ofattaining more than two logic states due to the nanoparticles ability toexhibit quantized charging. The basic design of memory devices isdescribed in further detail in U.S. Pat. No. 6,331,463 B1 which isincorporated herein by reference.

In some embodiments, the particles forming the floating gate 44 will besize-monodisperse with standard deviations approximately less than 10%about the mean diameter. These particle may organize spatially into alattice. In one embodiment, two or more distinct particle sizes willform the floating gate 44. These particles may organize spatially intobidisperse particle arrays. The particles making up the floating gate 44may be deposited by spin-coating, spraying from solution, sprayingthrough the rapid expansion from supercritical solution (RESS), or dropcasting. The particles in the floating gate 44 may be embedded in aconducting, or an insulating, polymer. In another embodiment, theparticles may be embedded in a thin gate oxide. In one embodiment, theparticles making up the floating gate 44 might be evaporated anddeposited from an aerosol. In embodiments with the floating gate 44consisting of distinct classes of sizes, for example, a bimodal sizedistribution of particles, discrete charging events may occur due to thesize dependence of the Coulomb charging of the particles. The termCoulomb charging refers to the repulsion between electrons within thenanoparticle core due to the small size of the particles. Coulombcharging leads to discrete voltage-dependent charging events, and may beutilized for multi valued logic applications, or other digitalapplications that use information stored as memory states higher thanbinary. A floating gate 44 may consist of a bimodal size distribution ofnanoparticles, either the Group IV particles described herein, orpossibly other nanoparticle materials, including ferromagnetic particlesand ferroelectric particles.

Light Emitting Devices

Other applications using nanoparticles exhibiting discrete opticalproperties may include light emitting devices and applications thereof.Specific interest has been focused on the development of inexpensive andefficient light emitting diodes (LEDs).

Light emitting devices such as light emitting diodes (LEDs) have beenconstructed in the past using P-doped and N-doped materials. However,such devices are generally only capable of emitting color of aparticular wavelength based on the semiconductor materials used in thediode. Light emitting devices have also been made using a polymericmaterial such as poly-(p-phenylene vinylene) (PPV) as a hole transportlayer between a hole injection electrode and an electron injectionelectrode. However, such devices are also limited to emission of asingle color, based on the type of light emitting polymeric materialutilized. Thus, to vary the color, one must use a different polymer,which prevents, or at least complicates, the display of light of variouscolors. Furthermore, since such polymeric materials do not function aselectron transport media, the recombination of holes and electrons,which results in such light emission, occurs adjacent the electroninjection electrode, which tends to lower the efficiency of the deviceas a light source.

Nanoparticles may be used in the formation of the emissive layer inLEDs. In one embodiment, silicon nanoparticles may be used in a lightemitting diode system. Silicon at nanometer dimensions has differentproperties than bulk silicon used in semiconductor chips. Bulk silicondoes not emit light; while, silicon nanoparticles at the sub-10nm levelmay exhibit luminescence over the entire visible spectrum. The specificwavelength emitted by the silicon nanoparticles may be dependent on thesize of the particles. For example, 10.5 nm silicon nanoparticles emitblue light; 8 nm silicon nanoparticles emit red light.

In an embodiment, running a current across an ordered distribution ofnanoparticles having particles having a average particle diameterbetween about 1.5 nm to about 8 nm. In one embodiment, variations involtage, however, may not effect the color of the light emitted by thenanoparticles. This embodiment may consist of a device withsize-monodisperse nanoparticles—i.e., particles with a standarddeviation about the mean diameter of 50% or less, or 20% or less, or 5%in some cases. In another embodiment, a device may emit voltage-tunablecolor. This device may consist of a mixture of particle sizes. Oneexample device might consist of a bimodal size distribution. Anotherexample device might have bimodal nanoparticles that are spatiallyorganized with either the small particles closer to the anode and thelarger particles closer to the cathode, or the small particles closer tothe cathode and the larger particles closer to the anode. In oneembodiment, the color of the emission is voltage tunable due to chargetransfer between the nanoparticles and the polymer. In this device, theparticles may be embedded in the polymer layer. In one embodiment, thenanoparticles may be sandwiched between a hole transporting layer and anelectron transporting layer. The charge transporting layers may beconducting polymers, or conducting small molecules, or molecularcrystals. In one embodiment, a gate electrode serves to modulate thecolor of light emission from the particles. A gate electrode may be usedto improve the efficiency of light emission in another embodiment.

In one embodiment, a light may be formed having a broad sizedistribution of silicon nanoparticles. The broad size distribution maybe advantageous in that the combination of wavelengths emitted by thedifferent size particles may produce a white light. The siliconnanoparticles may be embedded in a polymer matrix. The polymer matrix isnot, however, necessary for the silicon nanoparticles to functioneffectively as the emissive layer. The size distribution of siliconnanoparticles may allow the emission of white light. The nanoparticlesthemselves may emit with size-independent quantum yields and lifetimes.Clusters of nanoparticles may produce a broad emission band. If energytransfer occurs between neighboring nanoparticles, it does not result inthe selective emission from only the largest particles with the lowestenergy gap between the highest occupied and lowest unoccupied molecularorbitals (HOMO and LUMO). This situation is qualitatively different thanknown technology using CdSe nanoparticles.

FIG. 5 depicts an embodiment of a basic design for light emitting device52 including nanoparticles as described herein. light emitting device 52may include first electrode 54, second electrode 56, and emissive layer58. Emissive layer 58 may include the nanoparticles exhibiting discreteoptical properties as described herein. Emissive layer 58 may include apolymer wherein the nanoparticles may be suspended. However,nanoparticle based light emitting devices 52 may not require a polymerto emit, in contrast to many organic LEDs. Polymers may inflict lossesthrough absorption, scattering, and poor electron-hole interfaces.Emissive layer 58 may be positioned adjacent first electrode 54. Firstelectrode 54 may function as a cathode. Emissive layer 58 may bepositioned adjacent second electrode 56. Second electrode 56 mayfunction as an anode.

In an embodiment, second electrode 56 may include substrate 60.Substrate 60 may include a transparent conductive oxide layer.Non-limiting examples of the transparent conductive oxide layer mayinclude indium tin oxide, tin oxide, or a translucent thin layer of Nior Au or an alloy of Ni and Au. The basic design of light emittingdevices is described in further detail in U.S. Pat. No. 5,977,565 whichis incorporated herein by reference.

In an embodiment, the nanoparticles may emit light by opticalstimulation. In this device, an optical excitation source is used inplace of electrical stimulation. However, in another embodiment, acombination of optical excitation and electrical stimulation may be usedto enhance device performance, such as overall energy efficiency orperhaps color tenability.

Lasers

An extension of the application of nanoparticles in light emittingdevices is the use of nanoparticle based light emitting devices forcoherent light generation and optical gain applications. The basicproblem impeding the efficient operation of optically-pumped solid-statelasers is that the typical solid-state laser materials consist of a widebandgap insulating host material doped with optically active impurityatoms. The impurities are typically either rare-earth ions (Nd.sup.3+,Er.sup.3+) or the transition metals ions (Cr.sup.3+, Ti.sup.3+). Theabsorption spectrum of such ions is characterized by the linesassociated with the transitions between the shielded (and thus narrow) for d atomic levels. However, most of the pump sources for such lasers,such as high pressure gas discharge or incandescent lamps, arecharacterized by their extremely wide emission spectrum. Therefore, onlya small percentage of the pumped light is actually absorbed by the lasermaterial. For a small diameter laser rod, this is typically less than10%. As a result, the flashlamp pumped solid-state laser usuallyrequires a bulky power supply and a water cooled system. Besidesinefficiency, this renders the laser system useless for applicationswhere portability is a key requirement.

In recent years, the laser diode has emerged as a promising alternativeto flashlamp pumping of solid-state lasers. The high pumping efficiencycompared to flashlamps, stems from the better spectral match between thelaser-diode emission and the rare-earth absorption bands. As a result,the thermal load on both the laser rod and the pump is reduced. Thesystem weight and power consumption are also substantially reduced withincreased reliability. However, the cost of the diode laser arrays makesit expensive. In addition, the laser diodes require high current powersupplies that are usually heavy rendering the lasers impractical forairborne and space applications. Therefore, scientists have been tryingto harness an alternative energy pump source.

In response to the need for a more practical and efficient energy pumpsource the light emitting devices based on the nanoparticles describedherein may be used. In an embodiment, the nanoparticles may emit lightby optical stimulation. In this device, an optical excitation source isused in place of electrical stimulation. Optical excitation sources mayinclude natural sources such as sunlight or from manmade sources, forexample flashlamps. However, in another embodiment, a combination ofoptical excitation and electrical stimulation may be used to enhancedevice performance, such as overall energy efficiency or perhaps colortenability. Other sources of excitation include an electron beam from,for example, an electron gun.

In some embodiments, the nanoparticles may include doping agents toincrease efficiency. Examples of appropriate doping agents include rareearth ions and transition metal ions.

In certain embodiments, the nanoparticles may be coated or embedded inmaterials acting as a support for the nanoparticles. The supportmaterial may have a lower refractive index than that of thenanoparticles. The support material may also be transparent to theexciting radiation.

FIG. 9 depicts an embodiment of a basic design for laser assembly orcoherent light emitting device 78. Laser assembly 78 may includenanoparticle layers 80, substrate 82, mirrors 84 and 86 and lamp 88.Nanoparticle layers 80 may be positioned on substrate 82. Substrate 82may act as a support base for nanoparticle layers 80. Mirrors 84 and 86may form an optical cavity for laser assembly 78. Mirror 84 may bereflective towards radiation on the right side, effectively 100%. Theleft side of mirror 84 may or may not be reflective to assist incontrolling radiation entering the optical cavity. Mirror 86 may beslightly transparent (about 1%) to allow laser radiation between mirrors84 and 86 to exit as a beam in a controlled manner. Lamp 88 may bepositioned to illuminate nanoparticle layers 80 on substrate 82.Nanoparticle layers 80 absorb the light from lamp 88 exciting thenanoparticles causing the nanoparticles to emit light into the opticalcavity where it is trapped. The trapped light is then outputted as laserbeam 90 from mirror 86.

In some embodiments, nanoparticle layers 80 may be tailored to match theemission source. In an embodiment where the emission source is abroadband emission source, there may be multiple layers of nanoparticles80 as depicted in FIG. 9. As shown in FIG. 9 there may be fournanoparticle layers 80. In this embodiment, where the emission source isa low pressure gas discharge lamp (with a wide bandwidth emission),first nanoparticle layer 80 (first layer distinguished as being closestto lamp 88) may include relatively smaller sizes of the nanoparticlesdescribed herein. The result of using the smaller nanoparticles beingthat their bandgap is larger thereby lowering the absorption edge andrendering the layer more absorptive of the longer wavelength radiation.Second nanoparticle layer 80 (adjacent first nanoparticle layer 80), mayinclude nanoparticles of a somewhat larger size, with the result thatthe second layer will be more absorptive of shorter wavelengthradiation. Third nanoparticle layer 80 (adjacent second nanoparticlelayer 80), may include nanoparticles of a somewhat larger size than thesecond layer, with the result that the third layer will be moreabsorptive of shorter wavelength radiation than the second layer.Finally fourth nanoparticle layer 80 (positioned between the third layerand substrate 82) may have the largest nanoparticle sizes and thus willhave an absorption edge at the shortest wavelengths (which tend topenetrate deeper). In this way, more of the energy of the incidentradiation from lamp 88 will be absorbed thereby improving the absorptionefficiency of the system.

In other embodiments there may be fewer nanoparticle layers 80 (forexample, 1, 2, or 3) or there may be more than four nanoparticle layers80. The narrower the bandwidth of lamp 88, the fewer nanoparticle layers80 necessary. In other embodiments there may be only one nanoparticlelayer 80 including a wide distribution of size ranges to absorb abroader bandwidth of light Nanoparticle layers 80 may be oriented in anydirection and not necessarily the direction depicted in FIG. 9.

In other embodiments, an excitation source may be used to assist thenanoparticle layer(s) to emit light. The excitation source may includeany type of energy capable of inducing the nanoparticles to emit light.Non limiting examples of an excitation source are flashlamps, sunlight,and electricity.

FIG. 10 depicts an embodiment of a basic design for a laser using anelectrical excitation source. This embodiment traps light in an opticalcavity as described herein for the embodiment depicted in FIG. 9. Thedifference is that the nanoparticles are not excited optically butelectrically. In this embodiment a devise similar to light emittingdevice 52 described herein and depicted in FIG. 5 may be incorporated toemit the light which is trapped in the optical cavity. Light emittingdevice 52 may be electrically coupled to a power source (not shown).Multiple light emitting devices 52 may form an array between mirrors 84and 86. light emitting devices 52 may be oriented in any direction andnot necessarily the direction depicted in FIG. 10. The basic design ofcoherent light emitting devices (commonly known as lasers) and variousembodiments are described in further detail in U.S. Pat. No. 5,422,907which is incorporated herein by reference.

Various uses for the nanoparticle based lasers described herein may beenvisioned by those skilled in the art. An example of a use for thenanoparticle based laser may be as an optical switch in communicationsarrays or in information processing, for example in computers. Furthergeneral information regarding the structure and formation of opticalswitches may be found in U.S. Pat. No. 6,337,762 B1 which isincorporated herein by reference.

Displays

An extension of the application of nanoparticles in light emittingdevices is the use of nanoparticle based light emitting devices indisplay devices. Display devices, such as flat panel displays, arecurrently produced using liquid crystal technology. The current liquidcrystal technology currently in use in flat panel displays are limiteddue to manufacturing expense, high power consumption, and technicallimitations such as a relatively narrow viewing angle. Organic LEDs(OLED), molecular and polymer based, are also currently underconsideration as a replacement for the liquid crystal technology.Unfortunately, OLEDs are limited by short lifetimes and a catastrophicsensitivity to water and oxygen. OLED lifetimes decrease even more withincreasing brightness (and increasing current), which has relegated themto small display applications such as cell phone screens.

FIG. 6 depicts an embodiment of display 62 including a plurality oflight emitting devices that include nanoparticles as described herein.Display 62 may be a flat panel display. Display 62 may include a support64. The use of discrete nanoparticles may allow nanoparticle based lightemitting devices 52 to be mounted on flexible support 64. Flexiblesupport 64 may allow for the formation of a flexible display which mightbe more difficult to damage and easier to transport. The display mayinclude sets of different colored nanoparticle based light emittingdevices 52. Nanoparticle based light emitting devices 52 may function asdescribed herein. The colors of the nanoparticle based light emittingdevices 52 may include any combination of colors capable of producingalone or in combination the colors necessary for the envisionedapplication of display 62. Commonly used colors may include red, blue,and green.

In another embodiment, display 62 may include one or more layers ofcolored transparent layers of nanoparticle based light emitting devices52. The colored transparent layers of nanoparticle based light emittingdevices 52 may emit light alone or in combination to achieve colors notpossible when individual colored layers are used. The coloredtransparent layers of light emitting devices 52 may emit light from aportion of light emitting devices 52 within a particular layer or fromthe entire colored layer.

FIG. 7 depicts an embodiment of a basic design for a flat panel displayincluding multiple layers of transparent nanoparticle based lightemitting devices. Some embodiments of display 62 may include electricalconnectors that provide electrical power or signals to the individuallight emitting devices. The application or absence of an electricalsignal may determined whether the light emitting devices 52 emit lightor remain in an unlighted state.

In an embodiment, a display may include an input to receive displayinformation. The input may function to control the intensity of thelight emitted by the light emitting diodes. The input may function tocontrol the color of the light emitted by the display screen bycontrolling which of the light emitting devices are activated at a giventime. The input may control the color of the light emitted in any numberof ways. In one embodiment, one or more of several different coloredlight emitting devices may be signaled to emit simultaneously combiningto appear as if a different color, other than of the actual lightemitting devices themselves is being emitted. The input means mayfunction to control what portion of the light emitting devices formingthe array emit light.

Some embodiments of a display may include a transparent cover 66.Transparent cover 66 may be positioned over at least a portion of thelight emitting diodes forming the array. Transparent cover 66 mayfunction to assist in protecting portions of the display from physicaldamage. Transparent cover 66 may also serve additional functions such asreducing glare caused by lighting, natural or man made, not associatedwith the display panel itself.

Sensing Elements

There are many possible applications for the method and/or productsthereof described herein. In an embodiment, the nanoparticles may beused to provide information about a biological state or event or todetect an analyte in a fluid. Traditional methods for detectingbiological compounds in vivo and in vitro rely on the use of radioactivemarkers. These labels are effective because of the high degree ofsensitivity for the detection of radioactivity. However, many basicdifficulties exist with the use of radioisotopes. Such problems includethe need for specially trained personnel, general safety issues whenworking with radioactivity, inherently short half-lives with manycommonly used isotopes, and disposal problems due to full landfills andgovernmental regulations. As a result, current efforts have shifted toutilizing non-radioactive methods of detecting biological compounds.These methods often consist of the use of fluorescent molecules as tags(e.g. fluorescein, ethidium, methyl coumarin, and rhodamine) as a methodof detection. However, problems still exist when using these fluorescentmarkers. Problems include photobleaching, spectral separation, lowfluorescence intensity, short half-lives, broad spectral linewidths, andnon-gaussian asymmetric emission spectra having long tails.

Fluorescence is the emission of light resulting from the absorption ofradiation at one wavelength (excitation) followed by nearly immediatereradiation usually at a different wavelength (emission). Fluorescentdyes are frequently used as tags in biological systems. For example,compounds such as ethidium bromide, propidium iodide, Hoechst dyes(e.g., benzoxanthene yellow and bixbenzimide((2′-[4-hydroxyphenyl]-5-[4-methyl-1-piperazinyl]-2,5′-bi-1H-benzimidazol)and(2′-[4-ethoxyphenyl]-5-[4-methyl-1-piperazinyl]-2,5′-bi-1H-benzimidazol)),and DAPI (4,6-diamidino-2-phenylindole) interact with DNA and fluoresceto visualize DNA. Other biological components can be visualized byfluorescence using techniques such as immunofluorescence that utilizesantibodies labeled with a fluorescent tag and directed at a particularcellular target. For example, monoclonal or polyclonal antibodies taggedwith fluorescein or rhodamine can be directed to a desired cellulartarget and observed by fluorescence microscopy. An alternate method usessecondary antibodies that are tagged with a fluorescent marker anddirected to the primary antibodies to visualize the target.

There are chemical and physical limitations to the use of organicfluorescent dyes. One of these limitations is the variation ofexcitation wavelengths of different colored dyes. As a result,simultaneously using two or more fluorescent tags with differentexcitation wavelengths requires multiple excitation light sources. Thisrequirement thus adds to the cost and complexity of methods utilizingmultiple fluorescent dyes.

Another drawback when using organic dyes is the deterioration offluorescence intensity upon prolonged exposure to excitation light. Thisfading is called photobleaching and is dependent on the intensity of theexcitation light and the duration of the illumination. In addition,conversion of the dye into a nonfluorescent species is usuallyirreversible. Furthermore, the degradation products of dyes are organiccompounds that may interfere with biological processes being examined.

Another drawback of organic dyes is the spectral overlap that existsfrom one dye to another. This is due in part to the relatively wideemission spectra of organic dyes and the overlap of the spectra near thetailing region. Few low molecular weight dyes have a combination of alarge Stokes shift, which is defined as the separation of the absorptionand emission maxima, and high fluorescence output. In addition, lowmolecular weight dyes may be impractical for some applications becausethey do not provide a bright enough fluorescent signal. The idealfluorescent label should fulfill many requirements. Among the desiredqualities are the following: (i) high fluorescent intensity (fordetection in small quantities), (ii) a separation of at least 50 nmbetween the absorption and fluorescing frequencies, (iii) solubility inwater, (iv) ability to be readily linked to other molecules, (v)stability towards harsh conditions and high temperatures, (vi) asymmetric, nearly gaussian emission lineshape for easy deconvolution ofmultiple colors, and (vii) compatibility with automated analysis. Atpresent, none of the conventional fluorescent labels satisfies all theserequirements. Furthermore, the differences in the chemical properties ofstandard organic fluorescent dyes make multiple, parallel assays quiteimpractical since different chemical reactions may be involved for eachdye used in the variety of applications of fluorescent labels.

Thus, there is a need for a fluorescent label that satisfies theabove-described criteria for use in assay systems.

FIG. 8 depicts a schematic representation of an embodiment of ananoparticle labeled analyte. Sensing element 68 may include indicator70, receptor 72, and linker 74. Nanoparticles formed by any of themethods described herein may better satisfy the above criteria than morewidely known traditional methods. Sensing element 68 may include thenanoparticles as described herein and in some embodiments possess boththe ability to bind analyte 76 of interest and to create a signal.Sensing element 68 may include receptor molecules 72 which posses theability to bind analyte 76 of interest and to create a modulated signal.Alternatively, the sensing elements may include receptor molecules andindicators. The receptor molecule may posses the ability to bind to ananalyte of interest. Upon binding analyte 76, receptor 72 may causeindicator 70 to produce a signal. Receptor molecules 72 may be naturallyoccurring or synthetic receptors formed by rational design orcombinatorial methods.

Sensing element 68, in some embodiments, possesses both the ability tobind analyte 76 and to create a signal. Upon binding analyte of interest76, receptor molecule 72 may cause indicator molecule 70 to produce thesignal. Indicator 70 may produce a distinct signal in addition to thenanoparticles included in sensing element 68. In alternate embodimentsthe nanoparticles themselves may be use as indicator 70. Some examplesof natural receptors include, but are not limited to, DNA, RNA,proteins, enzymes, oligopeptides, antigens, and antibodies. Eithernatural or synthetic receptors may be chosen for their ability to bindto the analyte molecules in a specific manner. The forces which driveassociation/recognition between molecules include the hydrophobiceffect, anion-cation attraction, electrostatic attractions, covalentbinding, steric interactions, chiral interactions, and hydrogen bonding.The relative strengths of these forces depend upon factors such as thesolvent dielectric properties, the shape of the host molecule, and howit complements the guest. Upon host-guest association, attractiveinteractions occur and the molecules stick together. The most widelyused analogy for his chemical interaction is that of a “lock and key.”The fit of the key molecule (the guest) into the lock (the host) is amolecular recognition event.

Sensing element 68, in one embodiment, is capable of both binding theanalyte(s) of interest and creating a detectable signal. In oneembodiment, sensing element 68 will create an optical signal when boundto analyte of interest 76. In one embodiment, a detectable signal may becaused by the altering of the physical properties of indicator ligand 70bound to receptor 72. In one embodiment, two different indicators areattached to receptor 72. When analyte 76 is captured by receptor 72, thephysical distance between the two indicators may be altered such that achange in the spectroscopic properties of the indicators is produced.This process, known as Forster energy transfer, is extremely sensitiveto small changes in the distance between the indicator molecules. Inanother embodiment the optical signal might be created through electronor hole donation from the nanoparticle to the analyte, or from theanalyte to the nanoparticle. The analyte may quench the nanoparticlefluorescence. The nanoparticle may donate an electron to a redox activespecies in solution, which quenches that nanoparticle fluorescence, orchanges color to be detected by absorbance measurements, or may itselffluorescence or have its fluorescence quenched.

In one embodiment, a redox enzyme is attached via covalent ornoncovalent binding to the nanoparticle. The nanoparticle serves as aphotoreceptor. When light with sufficient energy shines on the particle,an exciton may form, or an excited electron, or an excited hole mightform. The electron or the hole may be transferred to the enzyme toprovide the energy necessary to drive an enzymatically catalyzed redoxreaction. The redox enzyme may be an NAD or NADH dependent enzyme, or anFAD or an FADH dependent enzyme. The enzyme may be stereospecific toproduce a desired stereoisomer.

In another embodiment, indicator ligand 70 may be preloaded onto thereceptor 72. Analyte 76 may then displace indicator ligand 70 to producea change in the spectroscopic properties of sensing elements 68. In thiscase, the initial background absorbance is relatively large anddecreases when analyte 76 is present. Indicator ligand 70, in oneembodiment, has a variety of spectroscopic properties in addition tothose imparted by the nanoparticles described herein which may bemeasured. These spectroscopic properties include, but are not limitedto, ultraviolet absorption, visible absorption, infrared absorption,fluorescence, and magnetic resonance. In one embodiment, the indicatoris a dye having either a strong fluorescence, a strong ultravioletabsorption, a strong visible absorption, or a combination of thesephysical properties. When indicator 70 is mixed with receptor, receptor72 and indicator 70 interact with each other such that the abovementioned spectroscopic properties of indicator 70, as well as otherspectroscopic properties may be altered. The nature of this interactionmay be a binding interaction, wherein indicator 70 and receptor 72 areattracted to each other with a sufficient force to allow the newlyformed receptor-indicator complex to function as a single unit. Thebinding of indicator 70 and receptor 72 to each other may take the formof a covalent bond, an ionic bond, a hydrogen bond, a van der Waalsinteraction, or a combination of these bonds.

For example, analytes 76 within a fluid may be derivatized with afluorescent tag before introducing the stream to sensing elements 76. Asanalyte molecules are adsorbed by the sensing element, the fluorescenceof the sensing element may increase. The presence of a fluorescentsignal may be used to determine the presence of a specific analyte.Additionally, the strength of the fluorescence may be used to determinethe amount of analyte 68 within the stream. The basic design of usingnanoparticles in biological assays is described in further detail inU.S. Pat. No. 6,306,610 B1 which is incorporated herein by reference.

Receptors

A variety of natural and synthetic receptors may be used. The syntheticreceptors may come from a variety of classes including, but not limitedto, polynucleotides (e.g., aptamers), peptides (e.g., enzymes andantibodies), synthetic receptors, polymeric unnatural biopolymers (e.g.,polythioureas, polyguanidiniums), and imprinted polymers. Natural basedsynthetic receptors include receptors which are structurally similar tonaturally occurring molecules. Polynucleotides are relatively smallfragments of DNA which may be derived by sequentially building the DNAsequence. Peptides may be synthesized from amino acids. Unnaturalbiopolymers are chemical structure which are based on naturalbiopolymers, but which are built from unnatural linking units. Unnaturalbiopolymers such as polythioureas and polyguanidiniums may besynthesized from diamines (i.e., compounds which include at least twoamine functional groups). These molecules are structurally similar tonaturally occurring receptors, (e.g., peptides). Some diamines may, inturn, be synthesized from amino acids. The use of amino acids as thebuilding blocks for these compounds allow a wide variety of molecularrecognition units to be devised. For example, the twenty natural aminoacids have side chains that possess hydrophobic residues, cationic andanionic residues, as well as hydrogen bonding groups. These side chainsmay provide a good chemical match to bind a large number of targets,from small molecules to large oligosaccharides.

In one embodiment, a polymer particle might be loaded withsuperparamagnetic particles, or ferromagnetic particles, or paramagneticparticles, that respond to applied magnetic fields. The Group IVnanoparticles might be attached to the magnetic polymer beads throughstandard chemistry. In one embodiment, the polymer particle serves as atransporter of the Group IV nanoparticles to desired locations. In oneembodiment, these materials might be used for therapeutic purposes. Amagnetic field may be applied to direct the nanoparticle location withinthe body. In one embodiment, the Group IV nanoparticles will serve asphotoreceptors for therapeutic purposes. Light might be shined on thepatient and absorbed by the particles to drive redox reactions withinthe body to destroy cancer cells. In another embodiment, heat might begenerated locally by the nanoparticles upon light absorption to destroythe neighboring cells. The light source for these applications may be anultrafast femtosecond laser, or a cw laser. Two photon absorption maylead to the therapeutic benefits of this treatment.

Linkers

In some embodiments, the receptor and/or indicators may be coupled tothe nanoparticles by a linker group. A variety of linker groups may beused. The term “linker”, as used herein, refers to a molecule that maybe used to link a receptor to an indicator; a receptor to a nanoparticleor another linker, or an indicator to a nanoparticle or another linker.A linker is a hetero or homobifunctional molecule that includes tworeactive sites capable of forming a covalent linkage with a receptor,indicator, other linker or nanoparticle. The capping agent describedherein may function as the linger. Suitable linkers are well known tothose of skill in the art and include, but are not limited to, straightor branched-chain carbon linkers, heterocyclic carbon linkers, orpeptide linkers. Particularly preferred linkers are capable of formingcovalent bonds to amino groups, carboxyl groups, or sulfhydryl groups orhydroxyl groups. Amino-binding linkers include reactive groups such ascarboxyl groups, isocyanates, isothiocyanates, esters, haloalkyls, andthe like. Carboxyl-binding linkers are capable of forming includereactive groups such as various amines, hydroxyls and the like.Sulfhydryl-binding linkers include reactive groups such as sulfhydrylgroups, acrylates, isothiocyanates, isocyanates and the like. Hydroxylbinding groups include reactive groups such as carboxyl groups,isocyanates, isothiocyanates, esters, haloalkyls, and the like. Incertain embodiments, an end of the linker is capable of binding to acrystalline composition formed from a Group IV metal element. The use ofsome such linkers is described in U.S. Pat. No. 6,037,137 which isincorporated herein by reference.

Biological Circuitry

In some embodiments, the nanoparticles may be coupled to a biologicalentity. The biological entity may be a cell, a nerve cell or a networkof neurons. The biological entity may be a skin cell, or a cell fromanother part of the body. The cell may be a single cell microorganism,or a mammalian cell. Connecting the nanoparticles to neurons, or otherbiological entities, may function in the same way as described hereinusing receptors and/or linkers. However, nanoparticles described hereinmay be capable of interacting electrically with cells. Nanoparticles mayinteract electrically with cells to provide stimulation. Upon lightabsorption, nanoparticles may generate local electric fields, or driveredox reactions at the cell surface, or create local pH gradients, whichmay affect the cell metabolism or the cell physiology. The localstimulation may induce the production of certain chemical productswithin the cell. The integration of biological systems andmicroelectronics offers a completely new strategy for next-generationheterojunction applications, such as neuronal memory devices andprosthetics that control cells directly. By using the appropriatereceptor the nanoparticle may be coupled to a specific type of cell orneuron or positioned at specific site on a cell. By using linkers withvery short length scales nanoparticles may be coupled to the cell withinnanometers of the cell surface. These linkers may be strands of RNA,DNA, short amino acid sequences, polypeptides, fatty acids, proteins,antibodies, or other small molecules. Positioning nanoparticles withinclose proximity to the cell reduces the deleterious effects of cellmembrane counter-ion charge screening. The particles may be coated withmolecules that induce the cellular uptake of the nanoparticles. In oneembodiment, the nanoparticles might be functionalized with a proteinsuch as transferring to enable cellular uptake. In another embodiment,the nanoparticles may be coated with molecular receptors that direct theplacement of the nanoparticles within the cell. Either within the cell,or adsorbed to the surface of the cell, optically activatednanoparticles experience electron-hole separation the nanoparticles mayproduce electric fields, or the potential to drive local redoxreactions, which may affect the viability of the cell, the metabolism,or metabolic products. Electric fields produced by nanoparticles mayinduce changes in the local cell potential, effectively forming anexample of biological circuitry.

Li Batteries

Lithium based batteries generally use electrolytes containing lithiumions. The anodes for these batteries may include lithium metal (lithiumbatteries), or compositions that intercalate lithium (lithium ionbatteries). The compositions that intercalate lithium, for use in thecathodes, generally are chalcogenides such as metal oxides that canincorporate the lithium ions into their lattice.

FIG. 11 depicts a schematic of an embodiment of a battery based on thenanoparticles described herein. A typical lithium battery 92 includes ananode 94, a cathode 96 and separator 98 between anode 94 and cathode 96.A single battery may include multiple cathodes and/or anodes.Electrolyte can be supplied in a variety of ways as described furtherbelow.

Lithium has been used in reduction/oxidation reactions in batteriesbecause they are the lightest metal and because they are the mostelectropositive metal. Metal oxides are known to incorporate lithiumions into their lattice structure through intercalation or similarmechanisms such as topochemical absorption. Thus, many metal oxides maybe effective as an electroactive material for a cathode in either alithium or lithium ion battery.

Lithium intercalated metal oxides are formed in the battery duringdischarge. The lithium leaves the lattice upon recharging, i.e., when avoltage is applied to the cell such that electric current flows into thecathode due to the application of an external current to the battery.Intercalation generally is reversible, making metal oxide based lithiumbatteries suitable for the production of secondary batteries.

In one embodiment, cathode 96 may include electroactive nanoparticlesheld together with a binder. Any of the nanoparticle described hereinmay be used in cathode 96 for lithium battery 92. For example, metaloxide nanoparticles produced using the methods described herein may beheld together with a binder to produce cathode 96. Nanoparticles for usein cathode 96 generally may have any shape, e.g., roughly sphericalnanoparticles or elongated nanoparticles. Cathode 96 may include amixture of different types of nanoparticles (e.g., vanadium oxide andtitanium oxide nanoparticles).

Cathode 96 optionally may include electrically conductive particles inaddition to the electroactive nanoparticles. These supplementary,electrically conductive particles generally are also held by the binder.Suitable electrically conductive particles include conductive carbonparticles such as carbon black, metal particles such as silver particlesand the like. These particles may also be nanoparticles, produced by anyof the methods described herein.

High loadings of nanoparticles can be achieved in the binder.Nanoparticles may make up greater than about 80 percent by weight of thecathode, and in some embodiments greater than about 90 percent byweight. The binder may be any of various suitable polymers such aspolyvinylidene fluoride, polyethylene oxide, polyethylene,polypropylene, polytetrafluoroethylene, polyacrylates and mixtures andcopolymers thereof.

Anode 94 of battery 92 may be constructed from a variety of materialsthat are suitable for use with lithium ion electrolytes. In the case oflithium batteries 92, anode 94 can include lithium metal or lithiumalloy metal either in the form of a foil, grid or metal particles in abinder.

Lithium ion batteries use particles having a composition that mayintercalate lithium. The particles may be held with a binder in theanode. Suitable intercalation compounds include, for example, graphite,synthetic graphite, coke, mesocarbons, doped carbons, fullerenes,niobium pentoxide and tin oxide,

Lithium batteries may also include collectors 100 that facilitate flowof electricity from the battery. Collectors 100 are electricallyconductive and may be made of metal such as nickel, iron, stainlesssteel, aluminum and copper and may be metal foil or preferably a metalgrid. Collector 100 may be on the surface of their associated electrodeor embedded within their associated electrode.

Separator 98 is an electrically insulating material that provides forpassage of at least some types of ions. Ionic transmission through theseparator provides for electrical neutrality in the different sectionsof the cell. Separator 98 generally prevents electroactive compounds incathode 96 from contacting electroactive compounds in anode 94.

A variety of materials may be used for separator 98. For example,separator 98 may be formed from glass fibers that form a porous matrix.Alternatively, separators 98 may be formed from polymers such as thosesuitable for use as binders. Polymer separators may be porous to providefor ionic conduction. Alternatively, polymer separators may be solidelectrolytes formed from polymers such as polyethylene oxide. Solidelectrolytes incorporate electrolyte into the polymer matrix to providefor ionic conduction without the need for liquid solvent.

Electrolytes for lithium batteries or lithium ion batteries may includeany of a variety of lithium salts. In some embodiments, lithium saltshave inert anions and are nontoxic. Suitable lithium salts include, butare not limited to, lithium hexafluorophosphate, lithiumhexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide), lithiumtrifluoromethane sulfonate, lithium tris(trifluoromethyl sulfonyl)methide, lithium tetrafluoroborate, lithium perchlorate, lithiumtetrachloroaluminate, lithium chloride and lithium perfluorobutane.

If a liquid solvent is used to dissolve the electrolyte, the solvent maybe inert and may not dissolve the electroactive materials. Generallyappropriate solvents include, but are not limited to, propylenecarbonate, dimethyl carbonate, diethyl carbonate, 2-methyltetrahydrofuran, dioxolane, tetrahydrofuran, 1,2-dimethoxyethane,ethylene carbonate, .gamma.-butyrolactone, dimethyl sulfoxide,acetonitrile, formamide, dimethylformamide and nitromethane.

The shape of the battery components may be adjusted to be suitable forthe desired final product, for example, a coin battery, a rectangularconstruction or a cylindrical battery. The battery generally includes acasing with appropriate portions in electrical contact with currentcollectors and/or electrodes of the battery. If a liquid electrolyte isused, the casing inhibits the leakage of the electrolyte. The casing mayhelp to maintain the battery elements in close proximity to each otherto reduce resistance within the battery. A plurality of battery cellsmay be placed in a single case with the cells connected either in seriesor in parallel. Further general information regarding the structure andformation of lithium batteries may be found in U.S. Pat. No. 6,130,007which is incorporated herein by reference.

EXAMPLES

The following examples are included to demonstrate certain embodiments.It should be appreciated by those of skill in the art that thetechniques disclosed in the examples which follow represent techniquesdiscovered which function well in the practice of the disclosure herein.However, those of skill in the art should, in light of the presentdisclosure, appreciate that many changes can be made in the specificembodiments which are disclosed and still obtain a like or similarresult without departing from the spirit and scope of the invention.

The following non-limiting examples demonstrate that by using a Sisurface-passivating solvent heated and pressurized, the necessarytemperatures can be reached to degrade the Si precursor whilemaintaining solvation of the capping ligand to arrest particle growth. Atemperature of 500° C. promotes Si crystallization. In certainembodiments a supercritical (sc) solvent can be used to provide asolvent with a high diffusion coefficient, on the order of 10⁻³ to 10⁻⁴cm² s⁻¹, for rapid reactant diffusion. Supercritical solvents may beused in preparation of narrow particle size distributions, in which theparticle growth is diffusion-limited. Using the methods of the inventionhighly stable Si nanoparticles ranging from approximately 10 to 200 Å indiameter can be produced.

Material and Methods

Diphenylsilane and anhydrous 1-octanol and hexane, packaged undernitrogen, were obtained from Aldrich Chemical Co. (St. Louis, Mo.) andstored in a nitrogen glovebox.

Organic-passivated Si nanoparticles were prepared by thermally degradingdiphenylsilane in mixtures of octanol and hexane (octanol:T_(c)=385°C.,P_(c)=34.5 bar, hexane: T_(c)=235° C., P_(c)=30 bar) well above thecritical point at 500° C. and 345 bar in an inconnell high-pressurecell. The presence of Si particles was observed by the formation of ayellow solution; no color change was observed in the absence ofdiphenylsilane. When diphenylsilane was degraded in the presence ofsc-ethanol rather than sc-octanol, the solution quickly turned fromorange to brown and then clear as polydisperse micron-sized Si particlesformed and settled on the walls of the reaction vessel. This resultsuggests that, unlike ethanol, the bound octanol chains providesufficient steric stabilization to prevent aggregation. The sc-octanolquenches the reaction and passivates the Si nanoparticle surface.

A typical preparation begins inside a glovebox. Diphenylsilane solution(250-500 mM in octanol) is loaded into an inconnell high-pressure cell(0.2 mL) and sealed under a nitrogen atmosphere. After removing the cellfrom the glovebox, it is attached via a three-way valve to a stainlesssteel high-pressure tube (˜40 cm³) equipped with a stainless steelpiston. Deionized water is pumped into the back of the piston with anHPLC pump (Thermoquest) to inject oxygen-free octanol through an inletheat exchanger and into the reaction cell to the desired pressure,between 140 and 345 bar. The cell is covered with heating tape (2 ft)and heated to 500° C. (±0.2° C.) within 15-20 min with use of a platinumresistance thermometer and a temperature controller. The reactionproceeds at these conditions for 2 h. Chloroform is used to extract theSi nanoparticles from the cell upon cooling and depressurization. Thenanoparticle dispersion is subsequently dried and the organic-stabilizedSi nanoparticles are redispersed in hexane or chloroform. The small 15 Ådiameter particles also redisperse in ethanol. The larger Sinanoparticles, with slightly broader size distributions, are produced byincreasing the Si:octanol mole ratio with hexane as a solvent; a typicalSi:octanol mole ratio is 1000:1. The reaction yield in percentconversion of Si precursor to Si incorporated in the nanoparticlesvaries from 0.5% to 5%.

In another experiment Si nanoparticles were synthesized via thermaldegradation of a silicon precursor in supercritical hexane. 1.5 mL of astock Si precursor solution (250 mM diphenylsilane and 25 mM octanethiolin hexane) was loaded into a 10 mL cylindrical titanium reactor in anitrogen glove box. All chemicals used for the synthesis were degassedto remove oxygen and stored in a nitrogen rich environment. The titaniumreactor was sealed, removed from the glove box, wrapped with hightemperature heating tape and heated to 500° C. The reaction proceeded at500° C. and 83 bar for 30 minutes. The reactor was then allowed to coolto room temperature over the course of approximately 2.5 hours. Theproduct was extracted with chloroform and precipitated in excess ethanolto remove reaction byproducts. The nanoparticles could be redispersed ina variey of organic solvents for further manipulation for lateranalysis.

A JEOL 2010 transmission electron microscope with 1.7 Å point-to-pointresolution operating with a 200 kV accelerating voltage with a GATANdigital photography system was used for transmission electronmicroscopy. In situ elemental analysis was performed on thenanoparticles with an Oxford energy dispersive spectrometer. Electrondiffraction images were obtained with the JEOL 2010 operating at 200 kV.Absorbance spectra were recorded with a Varian Cary 500 UV-Vis-NIRspectrophotometer with Si nanoparticles dispersed in ethanol or hexane.The extinction coefficients, ε, were determined for the nanoparticlesfrom the relationship between the measured absorbance (A=εcl), the pathlength (l=10 cm), and the Si concentration determined from dry weights.The quantity εc is the absorption coefficient, a Luminescencemeasurements were performed with a SpeX Fluorolog-3 spectrophotometer.The PL and PLE spectra were corrected with quinine sulfate as astandard. Quantum yields were calculated by comparison with 9,10diphenylanthracene. FTIR measurements were obtained with a Perkin-ElmerSpectrum 2000 FTIR spectrometer. FTIR spectra were acquired from driedfilms of silicon nanoparticles deposited on Zinc Selenide windows.

Example 1 Transmission Electron Microscopy

A TEM image of an organic-monolayer stabilized 40 Å diameter Sinanoparticle exhibits a crystalline core with a well-defined facetedsurface. The lattice spacing was 3.1 Å, characteristic of the distanceseparating the (111) planes in diamond-like Si. Si nanoparticle maypropagate through a radical mechanism as shown:Equation 1=(Ph)₂SiH₂→(Ph)₂SiH.Equation 2=2(Ph)₂SiH.→H(Ph)₂Si—Si(Ph)₂HThe benzene rings may help stabilize the diphenylsilane radicalintermediates by delocalizing the electron charge. These free radicalscan react to form Si—Si bonds. The octanol molecules subsequentlydisplace the phenyl groups and cap the Si particle surface. There areother possible mechanisms that include the formation and degradation ofother intermediate products, such as triphenyl and tetraphenyl silane.Furthermore, this reaction may not proceed through a free radicalmechanism.

Example 2 Extraction of Silicon Nanoparticles

Size-monodisperse 15 Å diameter Si nanoparticles were obtained byreacting diphenylsilane in pure octanol with subsequent redispersion inethanol. A fraction of the sample is made up of larger Si nanoparticlesthat form during the reaction that do not resuspend in ethanol due totheir hydrophobicity, whereas the extreme surface curvature of the 15 Ådiameter nanoparticles provides ethanol with “access” to the polarSi—O—C capping layer termination to enable the size-selective dispersionof 15 Å diameter Si nanoparticles. The 15 Å diameter nanoparticles arebarely perceptible in TEM images obtained with samples dispersed on acarbon-coated TEM grid. Low-resolution images of aggregates of these 15Å diameter nanoparticles show that the samples contain little sizevariation. For comparison, TEM images of larger Si nanoparticles withdiameters ranging from 25 to 35 Å produced by performing the synthesisin sc-hexane with increased Si:octanol mole ratios clearly reveal highlycrystalline cores and faceted surfaces. Crystalline lattice planes areobserved in nanoparticles as small as 25 Å. Electron diffraction fromthese nanoparticles also confirmed that the nanoparticles consist ofcrystalline Si cores with diamond lattice structure.

A variety of other techniques were used to characterize the Sinanoparticles, including, Fourier transform infrared spectroscopy(FTIR), UV-vis absorbance, and PL and PLE spectroscopy.

Example 3 In Situ Energy-Dispersive X-Ray Spectroscopy

In situ energy-dispersive X-ray spectroscopy (EDS) measurements of thenanoparticles imaged by TEM revealed Si in high abundance with thepresence of oxygen and carbon as well. A quantitative analysis of theelemental ratios was not possible since the supporting substrate wascarbon containing a measurable amount of residual oxygen.

FIG. 12 illustrates an example of energy-dispersive X-ray spectroscopy(EDS) analysis of an exemplary nanoparticle composition. The EDS data ofthe exemplary nanoparticle. The copper (Cu) peak results from the copperTEM grid used as a support. Other peaks shown are the carbon (C), oxygen(O) and silicon (Si) peak

Example 4 X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS), however, provides an elementalanalysis of the particles which gives an indication of how thenanoparticles are capped with the organic ligands. XPS data for 15 Ådiameter Si nanoparticles, which reveals that the sample contains a Si:Cratio of 0.70:1.

By using a shell approximation, d_(p)=a_(si)(3N_(si)/4π)^(1/3), wherea_(si) is the lattice constant (5.43 Å), the number of Si atoms, N_(si),in a nanoparticle can be calculated. Particles with 15 Å diameter(d_(p)) have approximately 88 atoms. The Si:C ratio determined from XPScan be used to calculate approximately the area occupied on thenanoparticle surface by each capping ligand. With the Si:C ratio equalto 0.7, the 15 Å cluster with 88 core Si atoms has 125 C atomssurrounding it. Each ligand has 8 carbons. Therefore, each particle issurrounded by approximately 16 capping ligands. Dividing the particlesurface area by 156 indicates that each ligand occupies an average of 44Å². This value is about twice that expected for a close-packed monolayerof ligands surrounding the nanoparticles. Therefore, XPS indicates thatthe ligands coat the nanoparticles with approximately 50% surfacecoverage. An estimate of the surface coverage of the largest 20 Ådiameter nanoparticles in the sample size distribution gives an area permolecule of 33 Å², for approximately 70% surface coverage. FIG. 13A andFIG. 13B illustrate examples of X-ray Photoelectron spectroscopy (XPS)analysis of an exemplary nanoparticle composition. In particular, XPS ofan exemplary 15 Å diameter silicon nanoparticles deposited on a graphitesubstrate. (A) Si 2p region in the spectrum (modified area is 592.2counts) and (B) Carbon 1s region (single line) and its deconvolutedpeaks from the graphite substrate (dashed line) and the capping ligand(dotted and dashed line). The modified area of the C Is curve due to thecapping ligand is 850.5 counts. The silicon-to-carbon ratio (Si:C) forthis particular example is 0.70:1.

Example 5 Fourier Transformed Infra-Red Spectroscopy

FTIR spectra show that the nanoparticles are most likely terminated witha combination of hydrogen and hydrocarbon chains, bound through analkoxide (Si—O—C) linkage. Four characteristic methylene and terminalmethyl stretching modes ν_(a(CH2))=2928 cm⁻¹, ν_(a(CH2))−2855 cm⁻¹,ν_(a)(CH₃jp)=2954.5 cm⁻¹, ν_(a)(CH₂FR)=2871 cm⁻¹, reveal that ahydrocarbon steric layer has indeed adsorbed to the particle surface.The notable absence of the hydroxyl stretch (ν_((O—H))=3300 cm⁻¹) andthe presence of the strong doublet corresponding to the Si—O—CH₂—stretching modes, v_((Si—O—CH2—))=1100-1070 cm⁻¹, suggests covalentalkoxide bonding to the Si nanoparticle surface. Siloxane Si—O—Sistretches typically occur at slightly lower wavenumber (1085 and 1020cm⁻¹); however, the presence of residual oxide on the nanoparticlesurfaces cannot be completely excluded based on these data alone. Theabsence of the very strong characteristic aryl-Si stretching mode, atv_((Si—Ph))=1125-1090 cm⁻¹, confirms precursor degradation. The lack ofthe strong v_((Si—C—Si))=1080-1040 cm⁻¹ stretching mode eliminates thepossibility that the Nanoparticles consist of a Si—C core, or that thealkane layer is directly adsorbed to the Si surface. Strong Si TO(transverse optical) phonon bands occur between 450 and 520 cm⁻¹,indicating that the particles are composed of Si only. Strong peaksbetween 750 and 850 cm⁻¹ can possibly be assigned to a variety of Si—Hstretching modes. There is also a possible carbonyl stretch at v_(—)1700cm⁻¹ that could result from octanol adsorption through a Si—C═O linkageif alcohol oxidation to the aldehyde occurs. On the basis of XPS andFTIR data, the nanoparticle surface is coated mostly by the hydrocarbonligands. However, the remaining 30% to 50% of the surface is coated witha combination of hydrogen, Si—C═O, and possibly a small portion ofoxide.

FIG. 14 illustrates an example of Fourier transformed infraredspectroscopy (FTIR) analysis of an exemplary nanoparticle composition.The spectrum reveals that the sterically stabilizing hydrocarbon chainsare covalently linked to the Si surface through alkoxide linkages. Thesecovalent linkages give rise to highly stable optical properties in thepresence of ambient oxygen and water.

Example 6 Optical Properties

The Si nanoparticles photoluminesce with overall quantum yields as highas 23% at room temperature. Several closely spaced discrete featuresappear in the PLE spectra of the 15 Å diameter nanoparticles, which aremirrored by a few meV in the absorbance spectra. The nanoparticlesexhibit size-dependent PL and PLE spectra, with the smallernanoparticles (approximately 15 Å diameter) emitting in the near-UV andthe larger nanoparticles (approximately 25 to 40 Å diameter) emittinggreen light. For all sizes, the absorption coefficient α was found toincrease quadratically with incident energy, α˜[hv−E₂]², near theabsorption edge, which is characteristic of a predominantly indirecttransition. Comparison of the extinction coefficients for bulk Si withthose measured for the 15 Å diameter nanoparticles. The indirect Γ→Xtransition remains the lowest energy transition, increasing from 1.2 eV(bulk Si) to 1.9 eV due to quantum confinement. It should be noted thatit appears that the direct Γ→Γ transition has red shifted to 3.2 eV from3.4 eV and the L→L transition energy has blue-shifted from 4.4 eV to 4.7eV, in quantitative agreement with empirical pseudopotentialcalculations by Ramakrishna and Friesner, although these assignmentscannot be made conclusively. Further comparison of the extinctioncoefficients measured for the nanoparticles with values for bulk Sireveals an overall lifting of the critical point degeneracies (directtransitions at k=0 and away from k=0), as predicted by both empiricalpseudopotential and tight-binding calculations, and an oscillatorstrength enhancement. These results contrast the spectra for slightlylarger, more polydisperse Si nanoparticles, ranging in size from 25 to40 Å in diameter, which exhibit monotonically increasing featurelessabsorbance spectra. A slight exciton peak, however, does seem to appearin the PLE spectra for the larger nanoparticles at 2.6 eV (470 nm).

The Si nanoparticle PL was remarkably stable in the presence ofatmospheric oxygen, especially when considering the sensitivity of theoptical properties of porous-Si to surface chemistry, such as oxidation.The sc-technique provides Si nanoparticles with sufficiently robustsurface passivation to prevent strong interactions between the Si coresand the surrounding solvent to enable efficient luminescence from Si.Comparison between the PL and PLE spectra reveals a Stokes shift ofapproximately 100 meV with respect to the lowest energy peak in the PLEspectra. The relatively broad PL peak has a characteristic lifetime of 2ns, indicating that various nonradiative processes are important in thenanoparticles. It is worth noting that the low-energy PL peak observedby Brus et al. for ˜20 Å diameter oxide-coated Si nanoparticles at 1.6eV was not observed in any of these samples.

FIG. 15 illustrates an example of photoluminescence (PL) andphotoluminescence excitation (PLE) spectral analysis of exemplarynanoparticle compositions. Room temperature PL are depicted as solidlines with the excitation energy marked by a solid arrow and PLE aredepicted as dashed lines with the detection energy marked by dashedarrows. The spectra of exemplary 15 Å nanoparticles are compared withspectra of slightly larger particles with a broader size distribution.

FIG. 16 illustrates an example of an absorbance profile of exemplarynanoparticle compositions. The absorbance spectra were insensitive tosolvent polarity, indicating that the absorbance is due to an excitonstate and not a charge-transfer transition between bound ligands. Motethe blue shift in the absorbance edge, and the appearance of discreteoptical transitions in the spectra of exemplary 15 Å nanoparticlescompared to the larger, more polydisperse nanoparticles.

FIG. 17 illustrates a comparison between the extinction coefficients ofbulk silicon as compared to the extinction coefficient of an exemplarynanoparticle composition. The absorption edge corresponds to theindirect Γ to X transition and the two peaks in the bulk Si spectracorrespond to the Γ to Γ and L to L critical points at 3.4 and 4.3 eV,respectively. Note the apparent blue shift of the Γ to X and L to Ltransitions in the nanoparticles due to quantum confinement and theapparent red shift of the Γ to Γ transition, as predicted by Ramakrishnaand Friesner, 1992.

FIG. 21 illustrates four single dot PL spectra of four differentnanoparticles at room temperature, showing the narrow line widths. Thepeak widths are very sharp compared to previously studiednanocrystalline silicon. Inset: Mean spectral trajectory of a singleparticle showing that spectral diffusion is not observable within theexperimental accuracy of the instrumentation

The origin of the photoluminescence in Si nanoparticles is quite complexand remains actively debated. The PL spectrum is clearly size dependent,with the larger particles emitting lower energy light than the smallerparticles, consistent with the general perception of quantum confinementeffects in Si. The PL from Si nanoparticles, however, has been shown tobe highly sensitive to surface chemistry, especially the presence ofoxide on the nanoparticle surface. Indeed, the PL spectrum of the 15 Ådiameter nanoparticles is complicated by the presence of two prominentpeaks in the 15 Å nanoparticle spectrum: one at 2.95 eV (419 nm) and oneat 2.65 eV (467 nm). Furthermore, the PL was found to depend on theexcitation wavelength, with 3.4 eV (363 nm) excitation yielding thehighest quantum yield and the sharpest PL. Increasing the excitationenergy from 3.4 eV to 4.4 eV (281 nm) led to a decrease in the intensityof the highest energy feature with respect to the low-energy “satellite”peak, and a decrease in the overall quantum yield. Although the peakscannot be assigned conclusively at this time, it can be proposed thatthe higher energy peak is intrinsic to quantum confinement in Sinanoparticles and the lower energy peak results from the presence ofoxygen on the particle surface. Calculation of the PL energy due tointrinsic quantum confinement in Si can in some cases differ from the PLenergy due to surface states, specifically Si═O. For nanoparticlesgreater than 3 nm in diameter, the intrinsic and surface state emissionenergies are the same, with emission at 2 eV (620 nm). However, 15 Ådiameter nanoparticles were predicted to give rise to intrinsic PL at2.8 eV, and surface state PL resulting from the presence of oxygen at2.3 eV (537 nm). The PL spectra of the Si nanoparticles are consistentwith this interpretation. It should be noted, however, that peaksplitting due to separate direct and phonon-assisted absorption andemission events has been observed for porous Si and may provide analternative explanation.

Example 7 Single Dot Spectroscopy Methods

Single dot spectroscopy measurements were conducted using a confocaloptical microscope in an epi-illumination configuration. Samples consistof Si nanoparticles dispersed on a glass coverslip by spin coating verydilute nanoparticle suspension in chloroform. The excitation laser beamfrom an Ar+ laser was focused by an oil immersion objective (1.2 NA) toa diffraction limited spot on the sample coverslip. Acomputer-controlled piezo stage scans the sample. The samplephotoluminescence was collected through the same objective, filteredwith a holographic notch filter to remove residual excitation light, anddetected by an avalanche photodiode (APD). Alternatively, the emissionspectra are obtained by directing the light output to a polychromatorequipped with an intensified charged-coupled device (ICCD) to record theintensity as a function of wavelength.

In order to obtain PL spectra from individual Si nanoparticles with arange of sizes in a single experiment, octanethiol-coated Sinanoparticles were synthesized with a broad size distribution, having anaverage diameter of 4.65±1.36 nm as determined by TEM (based on 361dots) and 4.35±2.02 nm determined by AFM height profiles of the sample(FIG. 24). The PL spectra obtained from the nanoparticles dispersed inchloroform were correspondingly broad. For example, the PL peak shown inFIG. 25 shifts as a function of excitation wavelength largely due to thebroad size distribution of the sample. At longer excitation wavelengths,only the larger nanoparticles with lower HOMO−LUMO energies are excitedand the emission peak shifts to longer wavelengths. The absorbancespectra and the photoluminescence excitation (PLE) spectra arefeatureless, due in part to the indirect nature of the Si band gap, butprimarily due to the broad size distribution of the nanoparticles. Atthe single particle level, however, the PL spectra is narrow, exhibitingpeaks with FWHM of 1596+/−502 cm⁻¹ (˜200 meV) (See FIG. 21).

As has been found for many single molecule systems, and othernanoparticles such as CdSe and InP, the Si nanoparticles exhibitfluorescence intermittency, or “blinking”, with a stochastic switchingon and off of the PL signal. Although the mechanism for blinking innanoparticles is not known, the “on” state can be viewed as an opticallycoupled ground and excited state, whereas the “off” state is aseptically“dark” state. The emission from a cluster of particles exhibitedintensity blinking against a gradually decaying background signal asshown in FIG. 26. One obvious test therefore involved the inspection ofthe time-resolved spectra for a gradually decaying background signal. Incases with few particles, a decaying background did not appear; however,the blinking behavior exhibited multiple intensity steps. In the singleparticle case, the blinking spectra clearly exhibited monotonictime-dependent PL intensities. As a secondary indicator, the PL peakenergy fluctuation was examined. When multiple particles produced theemission, the spectra fluctuated in energy as different sized particlesblinked on and off. Therefore, the blinking behavior and peakfluctuation were used to rigorously determine if the measured spectrawere truly a result of individual nanoparticles (See FIG. 27 throughFIG. 29).

The spectral line widths of the single Si dot PL were as narrow as 150meV. Although three times broader than the room temperature line widthsmeasured for single CdSe nanoparticles, these linewidths represent thenarrowest measured to dat for Si nanostructures. The four peaks shown inFIG. 21 represent typical narrow spectra measured from octanethiolcapped Si nanoparticles. Spectra determined to originate from individualnanoparticles did not show measurable spectal diffusion (FIG. 21 inset),suggesting that these organiocapped Si nanoparticles are stable againstdegradation in air. With excitation at 488 nm, the emission peak maximashift through the visible, from ˜525 nm up to ˜700 nm. Due toexperimental constraints, excitation wavelengths shorter than 488 nmwere not accessible, however, the ensemble spectra clearly show thatblue emission results from particles on the small end of the sizedistribution. Silicon can be made to emit visible light across allfrequencies in the visible spectrum by tuning the particle size. This israther remarkable, given that the bulk band gap of Si is in the near-IRat 1.1 eV.

In order to gain a better understanding of the nature of the lightemitting state in these organic-monolayer passivated nanoparticles, PLlifetimes were measured and the radiative rate was determined. 17Microsecond scale PL lifetime, observed previously in por-Si and oxidecapped Si nanoparticles, was not detected in our sample. Instead, it isestimated that 98±2% of the total PL exhibit a lifetime of less than orequal to 20 ns. FIG. 27 shows the time-resolved decay of the PL of theSi nanoparticles dispersed in chloroform. It was necessary to implementthree exponentials to fit the data: I(t)=A₁e^(−t/τ) ₁+A₂e^(−t/τ)₂+A₃e^(−t/τ) ₃, where I(t) is the measured PL intensity as a function oftime, t, after the excitation pulse. Table I (See FIG. 30) lists thefitted constants, A₁, A₂, A₃, τ₁, τ₂, τ₃, as a function of detectionwavelength. The octanethiol-capped Si nanoparticles examined hereexhibit characteristic lifetimes with a fast component (˜100 ps), andtwo slow components with lifetimes ranging from 2 to 6 ns—at least threeorders of magnitude faster than those previously found for por-Si and Sinanoparticles. Although the lifetimes of por-Si are characteristicallyorders of magnitude shorter than those of bulk Si—giving rise torelatively efficient PL—they are nonetheless characteristic of anindirect bandgap transition.

FIG. 28 depicts an example of an observation of “molecular” (

) and “continuum” (----) like single nanocrystal spectra Average of 37molecular type spectra and 31 continuum type spectra from singlenanoparticles excited at 488 nm. Each spectra was shifted so that itsmaximum was at zero before averaging. Histogram insets of spectralmaxima (λ_(max)) of continuum type and molecular type spectra,respectively.

FIG. 29 depicts an example of a comparison of the measured ensemblespectra (----) to the reconstructed ensemble spectra. reconstructed fromthe single dot spectra (

) of 68 individual silicon nanoparticles. As a last check to ensure thatthe single nanocrystal spectra presented in this study indeed representthe ensemble, the PL spectrum was reconstructed from the histogram of PLpeak intensity and position of individual nanoparticles. The ensemblespectra appear very similar to the reconstructed spectra, as shown inFIG. 29.

Example 8 Fluorescence Decay and Fluorescence Quantum Yield Measurements

Fluorescence decays were obtained by time-correlated single photoncounting (TCSPC) with 488-nm with vertically polarized excitation pulses(Δt˜200 fs, repetition rate 3.8 MHz) from a mode-locked Ti:sapphirelaser system (Coherent Mira 900, Coherent Pulse Picker Model 9200, InradSHG/THG model 5-050). Emission was collected at 900 with respect to theincident excitation axis through a Glan-Taylor polarizer set at the‘magic angle’ of 54.7°. Long pass filters and/or narrow bandinterference filters were used to block scattered laser light Detectionelectronics included a microchannel plate detector (HamamatsuR3809U-50), constant fraction discriminators (Tennelec TC454),time-to-amplitude converter (Tennelec TC864), and multichannel analyzer(Ortec TRUMP MCB). The emission wavelength was selected using 10nm-width bandpass filters. The emission decay curves were evaluated byan iterative nonlinear least squares fitting procedure. The decay datawas fit to a sum of exponential decays convoluted with the instrumentresponse (˜50 ps FW. The quality of the fit was evaluated by the reducedχ².

The fluorescence quantum yield of Si nanoparticles dispersed inchloroform was measured relative to Rhodamine 6G in ethanol (QY=95%)using 488 nm excitation on a fluorometer (SPEX) in a right-anglegeometry. The absorbance of both Si suspension and R6G solution at 488nm were adjusted to ˜0.06. The fluorescence spectra were corrected fordetector response.

Example 9 Formation of Sensing Elements/Analyte Complexes

Synthesis of CdS Quantum Dots (and Peptide Coated CdS Dots): Dots weresynthesized using previously published methods [H. M. Chen, X. F. Huang,L. Xu, J. Xu, K. J. Chen, D. Feng, Superlattices Microstruct. 2000, 27,1.]. Briefly, carboxyl-stabilized CdS nanoparticles were synthesized byarrested precipitation at room temperature in an aqueous solution usingmercaptoacetic acid as the colloidal stabilizer. All chemicals were usedas obtained from Sigma Chemical Co. (St Louis, Mo.). Nanoparticles wereprepared from a stirred solution of 0.036 g CdCl2 (1 mM) in 40 mL ofpure water. The pH was lowered to 2 with mercaptoacetic acid, and thenraised to 7 with concentrated NaOH. Then, 40 mL of 5 mM Na₂—S.9H₂O(0.023 g) was added to the mixture. The solution turned yellow shortlyafter sulfide addition due to CdS nanoparticle formation. For peptidecoated dots, peptide (0.041 mg/mL final solution) was added to thesolution until dissolved in the initial step (with the CdCl₂).Additional peptide densities were not tested, but will be the focus offuture studies aimed at improving binding between the cell and theqdots.

CdS Morbidity Studies: SK-N—SH neuroblastoma cells (American TypeCulture Collection #HTB-11) were incubated with CdS dots atconcentrations of 3×10⁻¹¹, 1.5×10⁻¹¹, and 0.75×10⁻¹¹ M in Dulbecco'sminimum essential medium (DMEM) cell culture medium (Sigma). Theseconcentrations reflect multiples of the relative number of qdots addedto the cells in the attachment procedure, up to ten times in excess.After adjustment to biocompatible salt concentrations (9 g/L), celldeath did not occur with CdS qdot addition. Cells were studied for fivedays for proliferation and attachment. No differences from controls wereobserved.

Conjugation of Quantum Dots to IgG Antibody: Goat IgG antibody (JacksonImmunochemistry) was covalently linked to CdS qdots at the carboxylterminus of the qdot capping ligands. Antibody was added to MES(2-N-morpholino) ethanesulfonic acid, Sigma) 50 mM buffer at aconcentration of 0.3 mg/mL. Then, an equal volume of 1.2 μM (80 mL batchdiluted to 480 mL) qdots was added to the solution. After a 15 minincubation period, EDAC (1-ethyl-3-(3-dimethylaminopropyl)-carbodiimidehydrochloride, Sigma) was added at 4 mg/mL. Next, the pH was adjusted topH6.5±0.2. Following 2 h in an orbital shaker, the reaction was quenchedusing glycine at 7.5 mg/mL. Conjugated qdots were isolated via repeatedcentrifugation (3000 g) and stored in phosphate buffered saline (PBS) atpH7.4. Control experiments exposing qdots to antibody without EDACrevealed noticeable physisorption of IgG on qdots, as evidenced bypellet formation during centrifugation. However, absorbance measurementsof these nanoparticles revealed substantially less IgG binding than inthe presence of EDAC. Raising the pH above 6.5, the physisorbed antibodydissociated from the nanoparticles. Therefore, prior to all nerve celllabeling experiments, the nanoparticles were transferred to 1 mL of PBS(pH 7.4). As a result of the crosslinking chemistry in the qdot±antibodyconjugation step, some agglomeration of particles occurred; however, theaggregates were small enough to remain suspended in solution.

Attachment of Quantum Dot-Complexes to Cells: Qdot-complexes wereattached to cells using standard immunocytology techniques [M. C.Willingham, in Methods in Molecular Biology, Vol. 115,Immunocytochemical Methods and Protocols (Ed: L. C. Javois), HumanaPress, Totowa, N.J. 1999, Ch. 16.]. Briefly, cells were placed on 22×22mm no. 1 thickness coverslips using imaging chambers (Sigma) to retainfluid. Cells were cultured in DMEM media (Sigma) at 37° C. and 5% CO₂ insterile conditions. After the cells attained ˜70% confluency, cells werewashed with 10 mM PBS (pH 7.4) five times. Then, the cells were blockedwith 5% bovine serum albumin (BSA) in PBS (BSA±PBS) for 30 min at 4° C.Following blocking, cells were washed five times in PBS. For antibodyattachment, primary antibody was added at 10 lg/mL in BSA±PBS andincubated for 30 min at 4° C. Cells were then washed five times withPBS. Then, antibody-qdot conjugate was added to cells to fill theimaging chamber (˜0.25 mL/chamber). Cells were incubated for 30 min at4° C. then washed with PBS five times. For peptide attachment, theimaging chamber was filled with peptide±qdot conjugate solution (˜0.25mL/chamber) taken from the 80 mL batch described above. Cells wereincubated for 30 min at 4° C., then washed five times with PBS.Following staining, cells ere stored in Dulbecco's PBS (with Ca²⁺ andMg²⁺, GIBCO) at 4° C.

FIG. 18 depicts an example of room temperature photoluminescence (PL)(λ_(exc)=400 nm) and photoluminescence excitation (PLE) (λ_(em)=600 nm)spectra of CdS qdots dispersed at pH 7.4 in PBS.

FIG. 19 depicts an example of room temperature absorbance spectrum of anaqueous dispersion of CdS qdots. The exciton peak at absorbance spectrumof an aqueous dispersion of CdS qdots. The exciton peak at 380 nm (3.6eV) corresponds to an average particle size of ˜30 angstroms.

FIG. 20 depicts an example of room temperature absorbance spectra of CdSqdots and CdS/antibody complexes. IgG absorbs at 280 nm (squares). Afterbinding IgG, the qdot absorbance spectrum (dashed) also exhibits thisfeature, which is absent in bare qdots (solid). Inset: CdS qdots boundto IgG (dashed) exhibit the same exciton peak as bare qdots (solid) at380 nm. The absorbance of antibody-qdot complexes is slightly reduceddue to less than 100% reaction yields. All materials were dispersed inPBS buffer (pH 7.4).

Example 10 Synthesis of Organic Monolayer-Stabilized CopperNanoparticles in Supercritical Water

Nanoparticle Synthesis: Copper(II) nitrate hemipentahydrate (Aldrich),copper(II) acetate monohydrate (Acros), and 1-hexanethiol (95%, Aldrich)were used as received without further purification. The experimentalapparatus consisted of a pumping system and a ⅞-in.-i.d., 4-in.-long 316stainless steel reaction cell (10 mL). For reactions without thiols, thecell was initially loaded at ambient conditions with 1.0 mL of purewater. For reactions with thiols, 900 μL of pure water with 100 μL of1-hexanethiol was used (initial water:thiol mole ratio ˜70:1). The cellwas sealed and heated to 400° C. and ˜173 bar using heating tape(Barnstead/Thermolyne) and an Omega temperature controller. The celltemperature was measured with a K-type thermocouple (Omega). A 0.02 Mcopper precursor solution was injected into the cell via 1/16-in.-i.d.stainless steel tubing by an HPLC pump (Beckman model 100A) at 4 mL/minuntil the operating pressure reached 413 bar. The solution reactsimmediately upon entering the reactor, as observed visually in aseparate experiment with an optical cell. The products precipitate uponcooling the reaction. The nanoparticles were removed from the cell witheither deionized water (uncapped particles) or chloroform (organiccapped particles). In the case of the thiol capped nanoparticles,unreacted precursor was removed by extraction with water. Thenanoparticles were filtered (Fisher, qualitative P5) to remove largeagglomerates of uncapped nanoparticles and dried using a rotaryevaporator (Buchi). The nanoparticles redisperse in either deionizedwater (uncapped particles) or chloroform (organic capped particles).

Phase Behavior of Supercritical Water and 1-Hexanethiol: The water and1-hexanethiol phase equilibria were studied in a titanium grade 2optical cell equipped with sapphire windows. Under the reactionconditions of 400° C. and ˜413 bar (50 μL of 1-hexanethiol in 150 μL ofwater), water and 1-hexanethiol are miscible. This miscibility isconsistent with the phase diagram for n-alkanes in water (n-pentane andn-heptane).

Characterization Method: Gas chromatography (GC) measurements ofhexanethiol were recorded with a Hewlett-Packard 5890A gas chromatographFourier transform infrared (FTIR) spectroscopy measurements wereperformed using a Perkin-Elmer Spectrum 2000 spectrometer with thenanoparticles dispensed on PTFE cards. Lowresolution transmissionelectron microscopy (TEM) images were obtained on a JEOL 200CXtransmission electron microscope operating with a 120-kV acceleratingvoltage, while high-resolution transmission electron microscopy (HRTEM)images and selected area electron diffraction (SAED) patterns wereobtained with a Gatan digital photography system on a JEOL 2010transmission electron microscope with 1.7-Å point-to-point resolutionoperated with a 200-kV accelerating voltage. All samples were preparedon Electron Microscope Sciences 200-mesh carbon-coated aluminum grids bydispersing suspended nanoparticles onto the grid and evaporating thesolvent. The measured lattice separations were indexed against standardsfor copper, Cu₂O, and CuO. UV-visible absorbance spectroscopy wasperformed using a Varian Cary 300 UV-visible spectrophotometer with thecapped nanoparticles dispersed in chloroform. X-ray photoelectronspectroscopy (XPS) was performed on a Physical Electronics XPS 5700,with a monochromatic Al X-ray source (Ka excitation at 1486.6 eV). ForXPS, the amples were deposited on a silicon wafer (cleaned with a 50:50mixture of ethanol/HCl), vacuum-dried at 25° C. to remove all residualsolvent, and stored under nitrogen.

FIG. 22 depicts examples of X-ray Photoelectron spectroscopy (XPS) ofuncapped particles produced via (a) Cu(NO₃)₂ and (b) Cu(CH₃COO)₂ and XPSscan of organically capped nanoparticles produced with (c) Cu(NO₃)₂ and(d) Cu(CH₃COO)₂. All scans are offset for clarity. Cu 2p core levelbinding energy for copper(II) at 934 eV and copper(0) at 932 eV.

FIG. 23 depicts an example of room-temperature UV-visible spectra oforganically capped copper nanoparticles synthesized via Cu(NO₃)₂ and1-hexanethiol.

Example 11 Electrogenerated Chemiluminescence from Nanopartidles

FIG. 31 depicts a schematic experimental setup for electrochemistry(such as cyclic voltammetry, differential pulse voltammetry) andelectrogenerated chemiluminescence (ECL) of Si nanoparticles. Acylindrical Pyrex vial 1.2 cm in diameter was used as electrochemicalcell, where a 1 or 2 mm Pt disk, Pt coil and silver wire served asworking (WE), counter (CE) and reference (RE) electrodes respectively.The ECL signal was recorded on the charge coupled device (CCD) camera.ECL could also be measured by a photomultiplier tube (PMT) and recordedas cyclic voltammetric ECL or ECL transients. The diagram belowillustrates the ECL process in the vicinity of the working electrodethrough annihilation of electrochemically produced anion and cationradicals by stepping to the reduction and oxidation potentialsalternatively.

FIG. 32 depicts cyclic voltammograms and differential pulsevoltammograms for several batches of Si nanoparticles in 0.1Mtetrahexylammonium perchlorate (THAP), N,N′-dimethylformamide (DMF)solution. The nanoparticles size and dispersion were (a) 2.77±0.37, (b)2.96±0.91 (c) 1.74±0.67 nm. Cyclic voltammetric ECL-voltage curves areplotted in (b) and (c). Dotted curves in (a) represent the response ofthe blank supporting electrolyte solution.

FIG. 33 depicts ECL transients for (a) annihilation of cation and anionradicals in 0.1 M THAP acetonitrile (MeCN) solution, (b) oxalatecoreactant system with 2.5 mM tetrabutyl ammonium oxalate added to thesolution of (a), and (c) persulfate coreactant system in 0.1M THAP DMFsolution with 6 mM tetrabutylammonium persulfate added. The size of thenanoparticles is around 2-4 nm in diameter.

FIG. 34 depicts ECL spectra for (a) annihilation of cation and anionradicals by stepping the potential between 2.7 and −2.1V at 10 Hz withintegration time 30 min in the same solution as FIG. 33(a), (b) oxalatecoreactant system, stepping the potential between 0.1 and 3V at 10 Hz;integration time 40 min in the same solution as FIG. 33(b), and (c)persulfate coreactant system, stepping the potential between −0.5 and−2.5V at 10 Hz; integration time 10 min in the same solution as FIG.33(c). The dotted curve in (c) is the ECL spectrum for the blanksolution.

FIG. 35 depicts (a) Schematic mechanisms for ECL and photoluminescence(PL) of Si clusters. (b) PLspectra at different excitation energyrecorded with the same solution as for FIG. 33(a). The excitationwavelength from top to bottom was between 360 and 520 nm at 20 nmintervals.

Sterically stabilized silicon nanoparticles are chemically stable underelectrochemical electron and hole injection. Differential pulsevoltammetry reveals a large electrochemical gap separating the onset ofelectron and hole injection, related to the sizedependent HOMO-LUMO gap,and discrete charging events with increased electron injection due toCoulomb blockade effects. The negatively and positively chargednanoparticles produced visible light upon electron transfer betweennanoparticles, or nanoparticles and redox active coreactants, insolution. This is the first example of electrogeneratedchemiluminescence from semiconductor nanoparticles. The energeticdifference between ECL and PL is believed to result from the greatersensitivity of the electron and hole wave functions with surface statesduring electrochemical charge transfer compared to optical excitation.These results reveal that nanoparticles of the elemental semiconductor,silicon, are more chemically robust than the compound semiconductornanoparticles studied to date. The silicon nanoparticles have theability to store charge in solution, which can subsequently lead tolight emission upon electron and/or hole transfer. This quality provideselectrochemically sensitive optoelectronic properties that may findfuture use in new sensor technologies.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements described herein withoutdeparting from the spirit and scope of the invention as described in thefollowing claims.

Example 12

The following example utilizes silicon nanoparticles that havehydrophobic organic ligands. The Si-nanoparticles were encapsulated inthe hydrophobic core of a micelle to make them water soluble, whilestill maintaining luminescence seen with the hydrophobicSi-nanoparticles dispersed in chloroform.

Experimental Procedure

First, octyl-β-D-glucopyranoside (detergent) was added toL-α-phosphatidycholine (lipid), both dispersed in chloroform. Next,silicon nanoparticles were added, also dispersed in chloroform, to thelipid/detergent mixture. After forming the lipid/detergent mixture,chloroform was removed by evaporation on a rotary evaporator, and thendistilled water was added. Lastly, the final solution was sonicateduntil an optically clear dispersion was obtained.

Results

An even dispersion of luminescence was seen under the UV lamp.Photoluminescence emission spectra showed that the nanoparticlesretained their luminescence in the aqueous environment, but the quantumyield drops by about a factor of 10. The silicon nanoparticles are watersoluble and still produce luminescence as shown in FIG. 36.

Another embodiment of the present invention is water-solublenanoparticles based on formation of liposome/detergent micelles fordispersion, wherein the nanoparticles are encapsulated in thehydrophobic core of a micelle and luminescence is maintained.Preferably, the Group IV nanoparticles are used, and preferably theGroup IV nanoparticles are coated with an organic layer. Preferably, theorganic layer is an alkene, more preferably octene or dodecene. Theouter organic layer of the nanoparticles can optionally further beovercoated with surfactants to allow water solubility.

Mixed micelles are formed with a mixture of one or more lipids a lipidand one or more detergents for encapsulation of Group IV nanoparticlesto form a stable dispersion in a polar solvent, including water,different alcohols, or acetone for example. Preferred lipids accordingto this embodiment of the invention include synthetic andnaturally-occurring lipids with anionic, cationic, zwitterionic ornon-ionic headgroups. The lipid headgroup may be attached to thehydrophobic tails by either ester or ether linkages. The detergents maybe anionic, cationic, zwitterionic or non-ionic, with either high or lowcritical micelle concentrations (CMCs). The lipids and detergents maycontain polymerizable headgroups, or tails. The surfactants may besingle-chained, such as sodium dodecyl suphate, stearic acid, hexadecyltrimethylammonium bromide, pentaoxyethylene dedecyl ether, orlysolecithin, or double-chained, such as phosphatidyl serine,phosphatidyl ethanolamine, phosphatidyl choline, lecithin, phosphatidicacid, aerosol OT, dihexadecyl dimethylammonium bromide,digalactosyldiglyceride or monogalactosyldiglyceride.

Still another embodiment of the present invention is a method ofdetermining the presence or absence of one or more target substances,comprising contacting a target area or sample which may contain thetarget substance or substances with an agent having affinity for thetarget substance or substances, wherein the affinity agent or agents arelinked to a luminescent nanoparticle, wherein said nanoparticle isencapsulated in a micelle, said micelle comprising at least onedetergent and at least one lipid; and examining the target area orsample for luminescence, said luminescence indicating that the targetsubstance is present. Such a method may be applied where the target areais in a living organism, making it possible, for example, to image adiseased area such as a tumor by selecting an affinity agent with theright affinity. The sample of this method may be a biological material,such as a blood, serum, or urine sample. Various affinity agents arewell known in the art which can be linked to the solubilizednanoparticles of the present invention, including antibodiestissue-specific liposomes.

In a preferred embodiment of this detection method, the target area orsample is examined for luminescence by applying energy capable ofexciting said nanoparticle to emit electromagnetic radiation anddetecting said electromagnetic radiation emitted by said nanoparticle.Preferably, the nanoparticles comprise a Group IV metal. Still morepreferably, the Group IV metal is silicon. In addition, thenanoparticles may be nanowires, including the nanowires described abovein the present specification.

Preferably, the nanoparticle is covalently linked to the affinity agent,though other linkages known in the art may be used depending on thenature of the detection method and how stable the linkage needs to be inthe environment of that detection method.

When silicon nanoparticles are used, an advantage of this detectionmethod is that silicon is generally regarded as a less toxic substancethan other semiconductor nanoparticles such as CdSe. Accordingly,silicon nanoparticles may advantageously be used for in vivo detectionmethods according to the invention.

Still another embodiment of the present invention is a method andcomposition for identifying a product or material utilizing thesolubilized luminescent nanoparticles of the invention. The solubilizednanoparticles can be dispersed in an area on the surface of the productor material and detected by applying energy which causes excitation ofthe nanoparticles that can be visually observed or detected bytechniques known in the art. Multiple sizes or types of solubilizednanoparticles may be used to create multiple colors.

For example, the pharmaceutical industry is losing huge sums of moneyeach year due to counterfeit pills. Marking the package with adetectable tag does not adequately address the problem becausecounterfeiters may simply remove the pills from the packaging. Thesolubilized luminescent nanoparticles of the present invention can beembedded in the surface coating put on pills and tablets, which is oftena sugar coating, or it may be dispersed within the same inertingredients in the core of a pill or tablet. They may also be embeddedin gel caps or in liquid medications, including suspensions.

Other areas in which solubilized nanoparticles may be used to helpidentify products and materials include tickets (such as those forsporting events, concerts, and theaters), media (including CDs,software, and DVDs), brand products (designer clothing and auto parts),identification (including drivers' licenses, medical ID, and passports),and financial products (including credit cards, bank checks, andcurrency).

When solubilized silicon nanoparticles are used for identifying productsor materials, one advantage is that they are very bright with goodefficiency in the near infra-red range. They also exhibit long lifetimesand may enable two-photon excitation. Silicon is the only phosphor thathas a red signature with UV absorption.

In this embodiment for identifying a product or material withsolubilized nanoparticles of the present invention, it is also possibleto “write” a desired label, such as a logo, product name, text or othersymbols utilizing the solubilized nanoparticles. This can beaccomplished by ink jet printing, stamping, or screen printing, forexample. The pattern or symbol may be used alone or together with auniform dispersion, where multiple colors are used to set apart thebackground dispersion color from the label color.

The present application further makes reference to the followingpublications, which are hereby expressly incorporated by reference intothe present application:

-   1. Dubertret, Benoit, et al., “In Vivo Imaging of Quantum Dots    Encapsulated in Phospholipid Micelles,” Science, 298, pp. 1759-62    (November 2002).-   2. Korgel, Brian A., et. al., “Synthesis of Size-Monodisperse CdS    Nanocrystals Using Phosphatidylcholine Vesicles as True Reaction    Compartments,” J. Phys. Chem. 100, pp. 346-51 (1996).-   3. Korgel, Brian A., et. al., “Vesicle Size Distributions Measured    by Flow Field-Flow Fractionation Coupled with Multiangle Light    Scattering,” Biophysical Journal 74, pp. 3264-72 (June 1998).

1. A composition of luminescent nanoparticles, wherein saidnanoparticles are encapsulated in micelles, said micelles comprising atleast one detergent and at least one lipid.
 2. A composition as claimedin claim 1, wherein the nanoparticles comprise a Group IV metal.
 3. Acomposition as claimed in claim 1, wherein the Group IV metal issilicon.
 4. A composition as claimed in claim 1, wherein thenanoparticles comprise a Group IV metal and a capping agent coupled tothe Group IV metal, wherein the nanoparticle has an average particlediameter of between about 1 to about 100 angstroms.
 5. A composition asclaimed in claim 1, wherein the nanoparticles are nanowires.
 6. A methodof determining the presence or absence of one or more target substances,comprising contacting a target area or sample which may contain thetarget substance or substances with an agent having affinity for thetarget substance or substances, wherein the affinity agent or agents arelinked to a luminescent nanoparticle, wherein said nanoparticle isencapsulated in a micelle, said micelle comprising at least onedetergent and at least one lipid; and examining the target area orsample for luminescence, said luminescence indicating that the targetsubstance is present.
 7. The method of claim 6, wherein the target areais in a living organism.
 8. The method of claim 6, wherein the sample isa biological material.
 9. The method of claim 6, wherein the target areaor sample is examined for luminescence by applying energy capable ofexciting said nanoparticle to emit electromagnetic radiation anddetecting said electromagnetic radiation emitted by said nanoparticle.10. The method of claim 6, wherein the nanoparticles comprise a Group IVmetal.
 11. The method of claim 10, wherein the Group IV metal issilicon.
 12. The method of claim 6, wherein the nanoparticles comprise aGroup IV metal and a capping agent coupled to the Group IV metal,wherein the nanoparticle has an average particle diameter of betweenabout 1 to about 100 angstroms.
 13. The method of claim 12, wherein thenanoparticles are nanowires.
 14. The method of claim 6, wherein thenanoparticle is covalently linked to the affinity agent.
 15. A method ofidentifying an article, comprising depositing a luminescent nanoparticleon a portion of the article, and detecting the presence or absence ofnanoparticles on the article based on luminescence.